Resist composition, method of forming resist pattern and polymeric compound

ABSTRACT

A resist composition including a base component (A) which exhibits changed solubility in a developing solution under action of acid and an acid-generator component (B) which generates acid upon exposure, wherein the base component (A) includes a polymeric compound (A1) having a structural unit (a5) represented by general formula (a5-1). In the formula (a5-1), R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; each of R a  and R b  independently represents a hydrocarbon group which may have a substituent, and R a  and R b  may be mutually bonded to form a ring.

TECHNICAL FIELD

The present invention is related to a resist composition and a method offorming a resist pattern, and a polymeric compound suited for the resistcomposition.

Priority is claimed on Japanese Patent Application No. 2011-006940,filed Jan. 17, 2011, the content of which is incorporated herein byreference.

BACKGROUND ART

In lithography techniques, for example, a resist film composed of aresist material is formed on a substrate, and the resist film issubjected to selective exposure of radial rays such as light or electronbeam through a mask having a predetermined pattern, followed bydevelopment, thereby forming a resist pattern having a predeterminedshape on the resist film.

A resist material in which the exposed portions become soluble in adeveloping solution is called a positive-type, and a resist material inwhich the exposed portions become insoluble in a developing solution iscalled a negative-type.

In recent years, in the production of semiconductor elements and liquidcrystal display elements, advances in lithography techniques have led torapid progress in the field of pattern miniaturization. Typically, theseminiaturization techniques involve shortening the wavelength (increasingthe energy) of the exposure light source. Conventionally, ultravioletradiation typified by g-line and i-line radiation has been used, butnowadays KrF excimer lasers and ArF excimer lasers are starting to beintroduced in mass production. Furthermore, research is also beingconducted into lithography techniques that use an exposure light sourcehaving a wavelength shorter (energy higher) than these excimer lasers,such as EB (electron beam), extreme ultraviolet radiation (EUV), and Xray.

As shortening the wavelength of the exposure light source progresses,resist materials for use with these types of exposure light sourcesrequire improvement in lithography properties such as a high resolutioncapable of reproducing patterns of minute dimensions, and a high levelof sensitivity to these types of exposure light sources. As a resistmaterial that satisfies these conditions, a chemically amplified resistcomposition is known,

For example, in the case where the developing solution is an alkalideveloping solution (alkali developing process), a chemically amplifiedresist composition which contains, as a base component (base resin), aresin which exhibits increased solubility in an alkali developingsolution under action of acid, and an acid generator is typically used.If the resist film formed using the chemically amplified resistcomposition is selectively exposed during formation of a resist pattern,then within the exposed portions, acid is generated from theacid-generator component, and the action of this acid causes an increasein the solubility of the resin component in an alkali developingsolution, making the exposed portions soluble in the alkali developingsolution. In this manner, the unexposed portions remain to form apositive resist pattern.

The base resin used exhibits increased polarity by the action of acid,thereby exhibiting increased solubility in an alkali developingsolution, whereas the solubility in an organic solvent is decreased.Therefore, when such a base resin is applied to a process using adeveloping solution containing an organic solvent (organic developingsolution) (hereafter, this process is referred to as “solvent developingprocess” or “negative tone-developing process”) instead of an alkalideveloping process, the solubility of the exposed portions of the resistfilm in an organic developing solution is decreased. As a result, theunexposed portions are dissolved and removed by the organic developingsolution, and a negative pattern in which the exposed portions remain isformed. The negative tone-developing process is proposed, for example,in Patent Document 1.

Currently, resins that contain structural units derived from(meth)acrylate esters within the main chain (acrylic resins) are nowused as base resins for chemically amplified resist compositions thatuse ArF excimer laser lithography, as they exhibit excellenttransparency in the vicinity of 193 nm (for example, see Patent Document2).

Here, the term “(meth)acrylic acid” is a generic term that includeseither or both of acrylic acid having a hydrogen atom bonded to theα-position and methacrylic acid having a methyl group bonded to theα-position. The term “(meth)acrylate ester” is a generic term thatincludes either or both of the acrylate ester having a hydrogen atombonded to the α-position and the methacrylate ester having a methylgroup bonded to the α-position. The term “(meth)acrylate” is a genericterm that includes either or both of the acrylate having a hydrogen atombonded to the α-position and the methacrylate having a methyl groupbonded to the α-position.

Furthermore, currently, in addition to the base resin and the acidgenerator, a nitrogen-containing organic compound such as an alkylamine,an alkylalcoholamine or the like is added to chemically amplified resistcompositions (for example, see Patent Documents 3 and 4). Thenitrogen-containing organic compound functions as a quencher which trapsthe acid generated from the acid generator, and contributes to improvingvarious lithography properties such as a pattern shape and the like.

DOCUMENTS OF RELATED ART Patent Documents

-   [Patent Document 1] Japanese Unexamined Patent Application, First    Publication No. 2008-292975-   [Patent Document 2] Japanese Unexamined Patent Application, First    Publication No. 2003-241385-   [Patent Document 3] Japanese Unexamined Patent Application, First    Publication No. H5-249662-   [Patent Document 4] Japanese Unexamined Patent Application, First    Publication No. H5-232706

SUMMARY OF THE INVENTION

As further progress is expected to be made in lithography techniques andthe application field for lithography techniques is expected to expand,development of a novel material for use in lithography will be desired.For example, as miniaturization of resist patterns progresses,improvement will be demanded for resist materials with respect tovarious lithography properties such as exposure latitude (EL), roughnessof the line width (line width roughness (LWR)) and the like, as well asresolution. The roughness, which refers to surface roughness of resistpatterns, becomes the cause of defects in the shape of the resistpattern. For example, roughness of the line width (LWR) can causevarious defects such as non-uniformity of the line width of line andspace patterns. Such defects adversely affect the formation of very finesemiconductor elements, and therefore, improvement thereof is importantas the resist pattern becomes more miniaturized.

The present invention takes the above circumstances into consideration,with an object of providing a resist composition which exhibitsexcellent lithography properties and enables formation of a resistpattern having an excellent shape, and a method of forming a resistpattern using the resist composition, and a polymeric compound suitedfor the resist composition.

For solving the above-mentioned problems, the present invention employsthe following aspects.

Specifically, a first aspect of the present invention is a resistcomposition including a base component (A) which exhibits changedsolubility in a developing solution under action of acid and anacid-generator component (B) which generates acid upon exposure, whereinthe base component (A) includes a polymeric compound (A1) having astructural unit (a5) represented by general formula (a5-1) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; eachof R^(a) and R^(b) independently represents a hydrocarbon group whichmay have a substituent, and R^(a) and R^(b) may be mutually bonded toform a ring.

A second aspect of the present invention is a method of forming a resistpattern, including: using a resist composition of the first aspect toform a resist film on a substrate; conducting exposure of the resistfilm; and alkali-developing the resist film to form a resist pattern.

A third aspect of the present invention is a polymeric compoundincluding a structural unit (a5) represented by general formula (a5-1)shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; eachof R^(a) and R^(b) independently represents a hydrocarbon group whichmay have a substituent, and R^(a) and R^(b) may be mutually bonded toform a ring.

In the present description and claims, the term “alkyl group” includeslinear, branched or cyclic, monovalent saturated hydrocarbon, unlessotherwise specified.

The term “alkylene group” includes linear, branched or cyclic divalentsaturated hydrocarbon, unless otherwise specified. The same applies forthe alkyl group within an alkoxy group.

A “fluorinated alkyl group” or a “fluorinated alkylene group” is a groupin which part or all of the hydrogen atoms of an alkyl group or analkylene group have been substituted with a fluorine atom.

A “lower alkyl group” is an alkyl group of 1 to 5 carbon atoms.

A “halogenated alkyl group” is a group in which part or all of thehydrogen atoms of an alkyl group are substituted with a halogen atom.Examples of the halogen atom include a fluorine atom, a chlorine atom, abromine atom and an iodine atom.

A “hydroxyalkyl group” is a group in which part or all of the hydrogenatoms of an alkyl group are substituted with a hydroxy group.

The term “aliphatic” is a relative concept used in relation to the term“aromatic”, and defines a group or compound that has no aromaticity.

The term “structural unit” refers to a monomer unit that contributes tothe formation of a polymeric compound (polymer, copolymer).

The term “exposure” is used as a general concept that includesirradiation with any form of radiation.

According to the present invention, there are provided a resistcomposition which exhibits excellent lithography properties and enablesformation of a resist pattern having an excellent shape, and a method offorming a resist pattern using the resist composition, and a polymericcompound suited for the resist composition.

MODE FOR CARRYING OUT THE INVENTION

<<Resist Composition>>

The resist composition of the present invention includes a basecomponent (A) which exhibits changed solubility in a developing solutionunder action of acid (hereafter, referred to as “component (A)”) and anacid-generator component (B) which generates acid upon exposure(hereafter, referred to as “component (B)”).

If the resist film formed using the resist composition is selectivelyexposed, then within the exposed portions, acid is generated from thecomponent (B), and the action of this acid causes a change in thesolubility of the component (A) in a developing solution, whereas thesolubility of the component (A) at the unexposed portions in adeveloping solution remains unchanged. Therefore, a difference of thesolubility between the exposed portions and the unexposed portions in adeveloping solution occurs. In this manner, the exposed portions aredissolved and removed by alkali developing of the resist film in thecase of a positive resist pattern, whereas unexposed portions aredissolved and removed in the case of a negative resist pattern, andhence, a resist pattern can be formed.

In the present specification, a resist composition which forms apositive resist pattern is called a positive resist composition, and aresist composition which forms a negative resist pattern is called anegative resist composition.

The resist composition of the present invention in the formation ofresist pattern may be used for an alkali developing process in which analkali developing solution is used in developing treatment, or a solventdeveloping process (this process is also referred to as “negativetone-developing process”) using a developing solution containing anorganic solvent (organic developing solution) in developing treatment.

<Component (A)>

The component (A) is a base component which exhibits changed solubilityin a developing solution under action of acid.

In the present description and claims, the term “base component” refersto an organic compound capable of forming a film, and an organiccompound having a molecular weight of 500 or more is preferably used asthe base component. When the organic compound has a molecular weight of500 or more, the organic compound exhibits a satisfactory film-formingability, and a resist pattern of nano level can be easily formed.

The “organic compound having a molecular weight of 500 or more” isbroadly classified into non-polymers and polymers.

In general, as a non-polymer, any of those which have a molecular weightin the range of 500 to less than 4,000 is used. Hereafter, a “lowmolecular weight compound” refers to a non-polymer having a molecularweight in the range of 500 to less than 4,000.

As a polymer, any of those which have a molecular weight of 1,000 ormore is generally used. In the present description and claims, the term“polymeric compound” or “resin” refers to a polymer having a molecularweight of 1,000 or more.

With respect to a polymeric compound, the “molecular weight” is theweight average molecular weight in terms of the polystyrene equivalentvalue determined by gel permeation chromatography (GPC).

In the present invention, the component (A) includes a polymericcompound (A1) (hereafter, referred to as “component (A1)”) having astructural unit (a5) represented by general formula (a5-1).

When the resist composition of the present invention is a “negativeresist composition for alkali developing process” which forms a negativepattern in an alkali developing process, for example, as the component(A), a base component that is soluble in an alkali developing solutionis used, and a cross-linking agent is blended in the negative resistcomposition.

In the negative resist composition for alkali developing process, whenacid is generated from the component (B) upon exposure, the action ofthe generated acid causes cross-linking between the base component andthe cross-linking agent, and the cross-linked portion becomes insolublein an alkali developing solution. Therefore, in the formation of aresist pattern, by conducting selective exposure of a resist film formedby applying the negative resist composition onto a substrate, theexposed portions become insoluble in an alkali developing solution,whereas the unexposed portions remain soluble in an alkali developingsolution, and hence, a resist pattern can be formed by alkalideveloping.

In the component (A) for a negative resist composition for alkalideveloping process, a resin that is soluble in an alkali developingsolution (hereafter, referred to as “alkali-soluble resin”) is used asthe component (A1).

As the cross-linking agent, at least one selected from the groupconsisting of a melamine-based cross-linking agent, a urea-basedcross-linking agent, an alkylene urea-based cross-linking agent, aglycoluril-based cross-linking agent and an epoxy-based cross-linkingagent is preferably used. Typically, a glycoluril-based cross-linkingagent having a methylol group or alkoxymethyl group, or themelamine-based cross-linking agent is preferable, as it enablesformation of a resist pattern with minimal swelling. The amount of thecross-linker added is preferably within a range from 1 to 50 parts byweight, relative to 100 parts by weight of the alkali-soluble resin.

In the case where the resist composition of the present invention is aresist composition which forms a positive pattern in an alkalideveloping process and a negative pattern in a solvent developingprocess, it is preferable to use a base component (A1) which exhibitsincreased polarity by the action of acid as the component (A). By usingthe base component which exhibits increased polarity by the action ofacid, since the polarity of the base component changes prior to andafter exposure, an excellent development contrast can be obtained notonly in an alkali developing process, but also in a solvent developingprocess.

More specifically, in the case of applying an alkali developing process,the component (A1) is substantially insoluble in an alkali developingsolution prior to exposure, but when acid is generated from thecomponent (B) upon exposure, the action of this acid causes an increasein the polarity of the base component, thereby increasing the solubilityof the component (A1) in an alkali developing solution. Therefore, inthe formation of a resist pattern, by conducting selective exposure of aresist film formed by applying the resist composition to a substrate,the exposed portions change from an insoluble state to a soluble statein an alkali developing solution, whereas the unexposed portions remaininsoluble in an alkali developing solution, and hence, a positive resistpattern can be formed by alkali developing.

On the other hand, in the case of a solvent developing process, thecomponent (A1) exhibits high solubility in an organic developingsolution prior to exposure, and when acid is generated from thecomponent (B) upon exposure, the polarity of the component (A1) isincreased by the action of the generated acid, thereby decreasing thesolubility of the component (A1) in an organic developing solution.Therefore, in the formation of a resist pattern, by conducting selectiveexposure of a resist film formed by applying the resist composition to asubstrate, the exposed portions change from a soluble state to aninsoluble state in an organic developing solution, whereas the unexposedportions remain soluble in an organic developing solution. As a result,by conducting development using an organic developing solution, acontrast can be made between the exposed portions and unexposedportions, thereby enabling the formation of a negative resist pattern.

In the present invention, the component (A1) preferably has, in additionto the structural unit (a5), a structural unit (a1) derived from anacrylate ester which may have the hydrogen atom bonded to the carbonatom on the α-position substituted with a substituent and containing anacid decomposable group which exhibits increased polarity by the actionof acid. That is, the resist composition of the present invention ispreferably a chemically amplified resist composition which becomes apositive type in the case of an alkali developing process, and anegative type in the case of a solvent developing process.

Further, the component (A1) preferably includes, in addition to thestructural unit (a5) and the structural unit (a1), at least onestructural unit selected from the group consisting of a structural unit(a0) derived from an acrylate ester which may have the hydrogen atombonded to the carbon atom on the α-position substituted with asubstituent and contains an —SO₂— containing cyclic group and astructural unit (a2) derived from an acrylate ester which may have thehydrogen atom bonded to the carbon atom on the α-position substitutedwith a substituent and contains a lactone-containing cyclic group.

Furthermore, it is preferable that the component (A1) include astructural unit (a3) derived from an acrylate ester which may have thehydrogen atom bonded to the carbon atom on the α-position substitutedwith a substituent and contains a polar group-containing aliphatichydrocarbon group and, as well as the structural unit (a5) and thestructural unit (a1), or the structural unit (a5), the structural unit(a1) and at least one structural unit selected from the group consistingof the structural unit (a0) and the structural unit (a2).

Here, in the present description and claims, a “structural unit derivedfrom an acrylate ester” refers to a structural unit that is formed bythe cleavage of the ethylenic double bond of an acrylate ester.

An “acrylate ester” refers to a compound in which the terminal hydrogenatom of the carboxy group of acrylic acid (CH₂═CH—COOH) has beensubstituted with an organic group.

The acrylate ester may have the hydrogen atom bonded to the carbon atomon the α-position substituted with a substituent. Examples of thesubstituent which substitutes the hydrogen bonded to the carbon atom onthe α-position include an alkyl group of 1 to 5 carbon atoms, ahalogenated alkyl group of 1 to 5 carbon atoms and a hydroxyalkyl group.The carbon atom on the α-position of an acrylate ester refers to thecarbon atom having the carbonyl group bonded thereto, unless specifiedotherwise.

Hereafter, an acrylate ester which has the hydrogen atom bonded to thecarbon atom on the α-position substituted with a substituent isfrequently referred to as an “a-position substituted acrylate ester”.Further, the acrylate ester and the α-position substituted acrylateester are included in and frequently referred to as an “(α-positionsubstituted) acrylate ester”.

With respect to the α-position substituted acrylate ester, the alkylgroup as the substituent at the α-position is preferably a linear orbranched alkyl group. Specific examples thereof include a methyl group,an ethyl group, a propyl group, an isopropyl group, an n-butyl group, anisobutyl group, a tert-butyl group, a pentyl group, an isopentyl group,and a neopentyl group and the like.

Specific examples of the halogenated alkyl group as the substituent atthe α-position include groups in which part or all of the hydrogen atomsof the aforementioned “alkyl group as the substituent at the α-position”are substituted with halogen atoms. Examples of the halogen atom includea fluorine atom, a chlorine atom, a bromine atom and an iodine atom, anda fluorine atom is particularly desirable.

It is preferable that a hydrogen atom, an alkyl group of 1 to 5 carbonatoms or a halogenated alkyl group of 1 to 5 carbon atoms be bonded tothe α-position of the α-position substituted acrylate ester, a hydrogenatom, an alkyl group of 1 to 5 carbon atoms or a fluorinated alkyl groupof 1 to 5 carbon atoms is more preferable, and in terms of industrialavailability, a hydrogen atom or a methyl group is the most desirable.

[Structural Unit (a5)]

The structural unit (a5) is a structural unit represented by theaforementioned general formula (a5-1).

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; eachof R^(a) and R^(b) independently represents a hydrocarbon group whichmay have a substituent, and R^(a) and R″ may be mutually bonded to forma ring.

In formula (a5-1), R represents a hydrogen atom, an alkyl group of 1 to5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms.

The alkyl group for R is preferably a linear or branched alkyl group,and specific examples include a methyl group, an ethyl group, a propylgroup, an isopropyl group, an n-butyl group, an isobutyl group, atert-butyl group, a pentyl group, an isopentyl group, and a neopentylgroup.

Examples of the halogenated alkyl group represented by R include a groupin which part or all of the hydrogen atoms of the aforementioned alkylgroup of 1 to 5 carbon atoms have been substituted with halogen atoms.Specific examples of the alkyl group include the same as theabove-mentioned alkyl group for R. Examples of the halogen atom whichsubstitutes the hydrogen of the alkyl group include a fluorine atom, achlorine atom, a bromine atom and an iodine atom, and a fluorine atom isparticularly desirable.

As R, a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or afluorinated alkyl group of 1 to 5 carbon atoms is preferable, and ahydrogen atom or a methyl group is particularly desirable in terms ofindustrial availability.

In formula (a5-1), each of R^(a) and R^(b) independently represents ahydrocarbon group which may have a substituent.

A hydrocarbon group “has a substituent” means that part or all of thehydrogen atoms within the hydrocarbon group are substituted withsubstituents (groups or atoms other than hydrogen).

The hydrocarbon group for each of R^(a) and R^(b) may be either analiphatic hydrocarbon group or an aromatic hydrocarbon group.

An “aliphatic hydrocarbon group” refers to a hydrocarbon group that hasno aromaticity.

The aliphatic hydrocarbon group may be saturated or unsaturated. Ingeneral, the aliphatic hydrocarbon group is preferably saturated.

As specific examples of the aliphatic hydrocarbon group, a linear orbranched aliphatic hydrocarbon group, and an aliphatic hydrocarbon groupcontaining a ring in the structure thereof can be given.

With respect to R^(a) and R^(b), the linear or branched aliphatichydrocarbon group preferably has 1 to 10 carbon atoms, more preferably 1to 8, still more preferably 1 to 5.

The linear or branched aliphatic hydrocarbon group may or may not have asubstituent. Examples of the substituent include a fluorine atom, afluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O).

With respect to R^(a) and R^(b), as examples of the hydrocarbon groupcontaining a ring in the structure thereof, an alicyclic hydrocarbongroup (a group in which one or more hydrogen atoms have been removedfrom an aliphatic hydrocarbon ring), a group in which the alicyclichydrocarbon group is bonded to the terminal of the linear or branchedaliphatic hydrocarbon group and a group in which the alicyclichydrocarbon group is interposed within the linear or branched aliphatichydrocarbon group, can be given. As examples of the linear or branchedaliphatic hydrocarbon group, the same groups as those described abovecan be given.

The alicyclic hydrocarbon group preferably has 3 to 20 carbon atoms, andmore preferably 3 to 12 carbon atoms.

The alicyclic hydrocarbon group may be either a polycyclic group or amonocyclic group. As the aliphatic hydrocarbon group for the monocyclicgroup, a group in which one or more hydrogen atoms have been removedfrom a monocycloalkane is preferable. The monocycloalkane preferably has3 to 6 carbon atoms, and specific examples thereof include cyclopentaneand cyclohexane. As the polycyclic group, a group in which one or morehydrogen atoms have been removed from a polycycloalkane is preferable,and the polycyclic group preferably has 7 to 12 carbon atoms. Examplesof the polycycloalkane include adamantane, norbornane, isobornane,tricyclodecane and tetracyclododecane.

The alicyclic hydrocarbon group may or may not have a substituent.Examples of the substituent include an alkyl group of 1 to 5 carbonatoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbonatoms, and an oxygen atom (═O).

With respect to R^(a) and R^(b), the aromatic hydrocarbon group is ahydrocarbon group having an aromatic ring.

The aromatic hydrocarbon group for R^(a) and R^(b) preferably has 3 to30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20,still more preferably 6 to 15, and most preferably 6 to 10. Here, thenumber of carbon atoms within a substituent(s) is not included in thenumber of carbon atoms of the aromatic hydrocarbon group.

Specific examples of the aromatic ring within the aromatic hydrocarbongroup include an aromatic hydrocarbon ring such as benzene, biphenyl,fluorene, naphthalene, anthracene, phenanthrene, and an aromatic heteroring in which part of the carbon atoms constituting the aromatichydrocarbon ring has been substituted with a heteroatom.

As examples of the heteroatom of the aromatic hetero ring, an oxygenatom, a sulfur atom and a nitrogen atom can be given.

Specific examples of aromatic hydrocarbon groups include a group (arylgroup) which is the aromatic hydrocarbon ring having one hydrogen atomremoved therefrom, and a group (for example, an arylalkyl group such asa benzyl group, a phenethyl group, a 1-naphthylmethyl group, a2-naphthylmethyl group, a 1-naphthylethyl group or a 2-naphthylethylgroup) in which one hydrogen atom of the aromatic hydrocarbon ring hasbeen substituted with an alkylene group. The alkylene group (an alkylchain within an arylalkyl group) preferably has 1 to 4 carbon atoms,more preferably 1 or 2, and most preferably 1.

The aromatic hydrocarbon group may or may not have a substituent. Forexample, a hydrogen atom bonded to the aromatic hydrocarbon ring withinthe aromatic hydrocarbon group may be substituted with a substituent. Asthe substituent, an alkyl group, an alkoxy group, a halogen atom, ahalogenated alkyl group, a hydroxyl group, an oxygen atom (═O) or thelike can be used.

The alkyl group as the substituent is preferably an alkyl group of 1 to5 carbon atoms, and a methyl group, an ethyl group, a propyl group, ann-butyl group or a tert-butyl group is particularly desirable.

The alkoxy group as the substituent for is preferably an alkoxy grouphaving 1 to 5 carbon atoms, more preferably a methoxy group, ethoxygroup, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxygroup, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom as the substituent for the aromatichydrocarbon group include a fluorine atom, a chlorine atom, a bromineatom and an iodine atom, and a fluorine atom is preferable.

An example of the halogenated alkyl group as the substituent includes agroup in which part or all of the hydrogen atoms within theaforementioned alkyl group have been substituted with the aforementionedhalogen atoms.

In formula (a5-1), R^(a) and R^(b) may be mutually bonded to form aring. The ring may be either a monocyclic group containing an N—C(═O)linkage or a polycyclic group containing an N—C(═O) linkage. Further,the ring may be a hetero ring in which part of the carbon atomsconstituting the ring has been substituted with a heteroatom. Asexamples of the heteroatom of the hetero ring, an oxygen atom, a sulfuratom and a nitrogen atom can be given.

Preferable examples of the structural unit (a5) include structural unitsrepresented by general formula (a5-1-1) shown below, since excellentlithography properties are readily obtained.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; Xrepresents CH₂, CH₂CH₂, O, S or SO₂; each of R^(c) and R^(d)independently represents a hydrocarbon group which may have asubstituent or a hydrogen atom, and R^(c) and R^(d) may be mutuallybonded to form a ring; p represents an integer of 0 to 3.

In formula (a5-1-1), R is the same as defined for R in theaforementioned formula (a5-1).

In formula (a5-1-1), X represents CH₂, CH₂CH₂, O, S or SO₂. Of these,CH₂ is particularly desirable.

In formula (a5-1-1), each of R^(e) and R^(d) independently represents ahydrocarbon group which may have a substituent or a hydrogen atom, andR^(c) and R^(d) may be mutually bonded to form a ring.

Here, the expression “may have a substituent” means that part or all ofthe hydrogen atoms of a hydrocarbon group may be substituted with asubstituent group (atoms other than hydrogen atoms, or groups).

The number of the substituent may be 1 or more.

The hydrocarbon group for each of R^(c) and R^(d) may be either analiphatic hydrocarbon group or an aromatic hydrocarbon group.

The aliphatic hydrocarbon group for each of R^(c) and R^(d) may beeither a saturated aliphatic hydrocarbon group, or an unsaturatedaliphatic hydrocarbon group. Further, such an aliphatic hydrocarbongroup may be linear, branched or cyclic.

As the aliphatic hydrocarbon group for R^(c) and R^(d), a linear orbranched saturated hydrocarbon group, a linear or branched monovalentunsaturated hydrocarbon group, or a cyclic aliphatic hydrocarbon group(aliphatic cyclic group) is preferable.

The linear saturated hydrocarbon group (alkyl group) preferably has 1 to20 carbon atoms, more preferably 1 to 15, and most preferably 1 to 10(here, the number of carbon atoms within a substituent(s) is notincluded in the number of carbon atoms of the hydrocarbon group).Specific examples include a methyl group, an ethyl group, a propylgroup, a butyl group, a pentyl group, a hexyl group, a heptyl group, anoctyl group, a nonyl group, a decanyl group, an undecyl group, a dodecylgroup, a tridecyl group, an isotridecyl group, a tetradecyl group, apentadecyl group, a hexadecyl group, an isohexadecyl group, a heptadecylgroup, an octadecyl group, a nonadecyl group, an icosyl group, ahenicosyl group and a docosyl group.

The branched saturated hydrocarbon group (alkyl group) preferably has 3to 20 carbon atoms, more preferably 3 to 15, and most preferably 3 to 10(here, the number of carbon atoms within a substituent(s) is notincluded in the number of carbon atoms of the hydrocarbon group).Specific examples include a 1-methylethyl group, a 1-methylpropyl group,a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group anda 4-methylpentyl group.

The unsaturated hydrocarbon group preferably has 2 to 10 carbon atoms,more preferably 2 to 5, and most preferably 2 to 4 (here, the number ofcarbon atoms within a substituent(s) is not included in the number ofcarbon atoms of the hydrocarbon group). Examples of linear monovalentunsaturated hydrocarbon groups include a vinyl group, a propenyl group,an allyl group (a 2-propenyl group) and a butynyl group. Examples ofbranched monovalent unsaturated hydrocarbon groups include a1-methylvinyl group (—C(CH₃)═CH₂), a 1-methylpropenyl group(—C(CH₃)═CH(CH₃)), a 2-methylpropenyl group (—CH═C(CH₃)₂) and a2-methyl-2-propenyl group (—CH₂—C(CH₃)═CH₂).

The cyclic aliphatic hydrocarbon group (aliphatic cyclic group) may beeither a monocyclic group or a polycyclic group. The aliphatic cyclicgroup preferably has 3 to 30 carbon atoms, more preferably 5 to 30,still more preferably 5 to 20, still more preferably 6 to 15, and mostpreferably 6 to 12 (here, the number of carbon atoms within asubstituent(s) is not included in the number of carbon atoms of thehydrocarbon group).

As the aliphatic cyclic group, a group in which one or more hydrogenatoms have been removed from a monocycloalkane or a polycycloalkane suchas a bicycloalkane, tricycloalkane or tetracycloalkane can be used.Specific examples include groups in which one or more hydrogen atomshave been removed from a monocycloalkane such as cyclopentane orcyclohexane; and groups in which one or more hydrogen atoms have beenremoved from a polycycloalkane such as adamantane, norbornane,isobornane, tricyclodecane or tetracyclododecane.

Of these, the aliphatic cyclic group is preferably a polycyclic group,more preferably a group in which one or more hydrogen atoms have beenremoved from a polycycloalkane, and a group in which one or morehydrogen atoms have been removed from adamantane is particularlydesirable.

Further, the aliphatic hydrocarbon group for R^(c) and R^(d) may be agroup in which the terminal of an alkylene group is bonded to analiphatic cyclic group. As examples of the aliphatic cyclic group, thesame aliphatic cyclic group as defined above can be given.

The aliphatic hydrocarbon group for R^(c) and R^(d) may have asubstituent. For example, part of the carbon atoms constituting thealiphatic hydrocarbon group may be substituted with a substituent groupcontaining a heteroatom, or part or all of the hydrogen atoms of thealiphatic hydrocarbon group may be substituted with a substituent group.

Here, as the “heteroatom”, there is no particular limitation as long asit is an atom other than carbon and hydrogen. Examples of heteroatomsinclude a halogen atom, an oxygen atom, a sulfur atom and a nitrogenatom. Examples of the halogen atom include a fluorine atom, a chlorineatom, an iodine atom and a bromine atom.

The substituent group containing a heteroatom may consist of aheteroatom, or may be a group containing a group or atom other than aheteroatom.

Specific examples of the substituent for substituting part of the carbonatoms constituting the aliphatic hydrocarbon group include —O—,—C(═O)—O—, —C(═O)—, —O—C(═O)—O—, —C(═O)—NH—, —NH— (the H may be replacedwith a substituent such as an alkyl group or an acyl group), —S—,—S(═O)₂— and —S(═O)₂—O—. When the aliphatic hydrocarbon group is cyclic(aliphatic cyclic group), the aliphatic hydrocarbon group may containany of these substituent groups in the ring structure.

Examples of the substituent group for substituting part or all of thehydrogen atoms of the aliphatic hydrocarbon group include an alkoxygroup, a halogen atom, a halogenated alkyl group, a hydroxyl group, anoxygen atom (═O) and a cyano group. The aforementioned alkoxy group ispreferably an alkoxy group having 1 to 5 carbon atoms, more preferably amethoxy group, ethoxy group, n-propoxy group, iso-propoxy group,n-butoxy group or tert-butoxy group, and most preferably a methoxy groupor an ethoxy group. Examples of the aforementioned halogen atom includea fluorine atom, a chlorine atom, a bromine atom and an iodine atom, anda fluorine atom is preferable. An example of the aforementionedhalogenated alkyl group includes a group in which part or all of thehydrogen atoms within an alkyl group of 1 to 5 carbon atoms (e.g., amethyl group, an ethyl group, a propyl group, an n-butyl group or atert-butyl group) have been substituted with the aforementioned halogenatoms. When the aliphatic hydrocarbon group is cyclic (aliphatic cyclicgroup), part or all of the hydrogen atoms of the aliphatic cyclic groupmay further be substituted with a alkyl group of 1 to 5 carbon atoms.

The aromatic hydrocarbon group for R^(c) and R^(d) is a hydrocarbongroup having an aromatic ring. The aromatic hydrocarbon ring preferablyhas 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably5 to 20, still more preferably 6 to 15, and most preferably 6 to 12.Here, the number of carbon atoms within a substituent(s) is not includedin the number of carbon atoms of the aromatic hydrocarbon group.

Specific examples of aromatic hydrocarbon groups include an aryl groupwhich is an aromatic hydrocarbon ring having one hydrogen atom removedtherefrom, such as a phenyl group, a biphenyl group, a fluorenyl group,a naphthyl group, an anthryl group or a phenanthryl group; and analkylaryl group such as a benzyl group, a phenethyl group, a1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethylgroup, or a 2-naphthylethyl group. The alkyl chain within the arylalkylgroup preferably has 1 to 4 carbon atoms, more preferably 1 or 2, andmost preferably 1.

The aromatic hydrocarbon group for R^(c) and R^(d) may have asubstituent. For example, part of the carbon atoms constituting thearomatic ring within the aromatic hydrocarbon group may be substitutedwith a heteroatom, or a hydrogen atom bonded to the aromatic ring withinthe aromatic hydrocarbon group may be substituted with a substituent.

In the former example, a heteroaryl group in which part of the carbonatoms constituting the ring within the aforementioned aryl group hasbeen substituted with a heteroatom such as an oxygen atom, a sulfur atomor a nitrogen atom, and a heteroarylalkyl group in which part of thecarbon atoms constituting the aromatic hydrocarbon ring within theaforementioned arylalkyl group has been substituted with theaforementioned heteroatom can be used.

In the latter example, as the substituent for the aromatic hydrocarbongroup, an alkyl group, an alkoxy group, a halogen atom, a halogenatedalkyl group, a hydroxyl group, an oxygen atom (═O) or the like can beused.

The alkyl group as the substituent for the aromatic hydrocarbon group ispreferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, anethyl group, a propyl group, an n-butyl group or a tert-butyl group ismore preferable.

The alkoxy group as the substituent for the aromatic hydrocarbon groupis preferably an alkoxy group having 1 to 5 carbon atoms, morepreferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxygroup, n-butoxy group or tert-butoxy group, and most preferably amethoxy group or an ethoxy group.

Examples of the halogen atom as the substituent for the aromatichydrocarbon group include a fluorine atom, a chlorine atom, a bromineatom and an iodine atom, and a fluorine atom is preferable.

An example of the halogenated alkyl group as the substituent for thearomatic hydrocarbon group includes a group in which part or all of thehydrogen atoms within the aforementioned alkyl group have beensubstituted with the aforementioned halogen atoms.

In formula (a5-1-1), R^(c) and R^(d) may be mutually bonded to form aring. For example, R^(c) and R^(d) each independently represents alinear or branched alkylene group, and the terminal of R^(c) is bondedto the terminal of R^(d) to form a ring. In such a case, a cyclic groupis formed by R^(c), the carbon atom having R^(c) bonded thereto, R^(d),and the carbon atom having R^(d) bonded thereto. Such a cyclic group ispreferably a 3- to 10-membered ring, and more preferably 4- to7-membered ring, and most preferably a 4- to 6-membered ring.

Among the above-mentioned examples, as R^(c) and R^(d), in terms ofstability and synthesis, preferably, R^(c) and R^(d) are mutually bondedto form a ring

In formula (a5-1-1), p represents an integer of 0 to 3. In terms ofstability, p is preferably 0 or 1, and 0 is particularly desirable.

Specific examples of structural unit (a5) are shown below. In theformulas shown below, R^(α) represents a hydrogen atom, a methyl groupor a trifluoromethyl group.

As the structural unit (a5) contained in the component (A1), one type ofstructural unit may be used, or two or more types may be used incombination.

Among the above-mentioned examples, the structural unit (a5) ispreferably a structural unit represented by the aforementioned generalformula (a5-1-1). Of these, at least one selected from the groupconsisting of structural units represented by chemical formulas(a5-1-11), (a5-1-12), (a5-1-14), (a5-1-15) and (a5-1-19) is morepreferable, and a structural unit represented by chemical formula(a5-1-11) is particularly desirable.

In the component (A1), the amount of the structural unit (a5) based onthe combined total of all structural units constituting the component(A1) is preferably 5 to 50 mol %, more preferably 7 to 45 mol %, stillmore preferably 10 to 40 mol %, and most preferably 20 to 40 mol %.

When the amount of the structural unit (a5) is at least as large as thelower limit of the above-mentioned range, diffusion of acid generatedupon exposure can readily be controlled using a resist compositionprepared from the component (A1), and lithography properties such as EL,LWR are improved. On the other hand, when the amount of the structuralunit (a5) is no more than the upper limit of the above-mentioned range,good balance can readily be achieved with the other structural units.

[Structural Unit (a1)]

The structural unit (a1) represents a structural unit derived from anacrylate ester which may have the hydrogen atom bonded to the carbonatom on the α-position substituted with a substituent and containing anacid decomposable group which exhibits increased polarity by the actionof acid.

The term “acid decomposable group” refers to a group in which at least apart of the bond within the structure thereof is cleaved by the actionof an acid generated from the component (B) upon exposure.

Examples of acid decomposable groups which exhibit increased polarity bythe action of an acid include groups which are decomposed by the actionof an acid to form a polar group.

Examples of the polar group include a carboxy group, a hydroxy group, anamino group and a sulfo group (—SO₃H). Among these, a polar groupcontaining —OH in the structure thereof (hereafter, referred to as“OH-containing polar group”) is preferable, a carboxy group or a hydroxygroup is more preferable, and a carboxy group is particularly desirable.

More specifically, as an example of an acid decomposable group, a groupin which the aforementioned polar group has been protected with an aciddissociable group (such as a group in which the hydrogen atom of theOH-containing polar group has been protected with an acid dissociablegroup) can be given.

An “acid dissociable group” is a group in which at least the bondbetween the acid dissociable group and the adjacent carbon atom iscleaved by the action of an acid generated from the component (B) uponexposure. It is necessary that the acid dissociable group thatconstitutes the acid decomposable group be a group which exhibits alower polarity than the polar group generated by the dissociation of theacid dissociable group. Thus, when the acid dissociable group isdissociated by the action of acid, a polar group exhibiting a higherpolarity than that of the acid dissociable group is generated, therebyincreasing the polarity. As a result, the polarity of the entirecomponent (A1) is increased. By the increase in the polarity, thesolubility in a developing solution is relatively changed. When thedeveloping solution is an alkali developing solution, the solubility inthe alkali developing solution is increased. On the other hand, when thedeveloping solution is a developing solution containing an organicsolvent (organic developing solution), the solubility in the organicdeveloping solution decreases.

As the acid dissociable group, there is no particular limitation, andany of the groups that have been proposed as acid dissociable groups forthe base resins of chemically amplified resists can be used. Generally,groups that form either a cyclic or chain-like tertiary alkyl ester withthe carboxyl group of the (meth)acrylic acid, and acetal-type aciddissociable groups such as alkoxyalkyl groups are widely known.

Here, a tertiary alkyl ester describes a structure in which an ester isformed by substituting the hydrogen atom of a carboxyl group with achain-like or cyclic tertiary alkyl group, and a tertiary carbon atomwithin the chain-like or cyclic tertiary alkyl group is bonded to theoxygen atom at the terminal of the carbonyloxy group (—C(═O)—O—). Inthis tertiary alkyl ester, the action of acid causes cleavage of thebond between the oxygen atom and the tertiary carbon atom, therebyforming a carboxy group.

The chain-like or cyclic alkyl group may have a substituent.

Hereafter, for the sake of simplicity, groups that exhibit aciddissociability as a result of the formation of a tertiary alkyl esterwith a carboxyl group are referred to as “tertiary alkyl ester-type aciddissociable groups”.

Examples of tertiary alkyl ester-type acid dissociable groups includealiphatic branched, acid dissociable groups and aliphatic cyclicgroup-containing acid dissociable groups.

Here, the term “aliphatic branched” refers to a branched structurehaving no aromaticity. The “aliphatic branched, acid dissociable group”is not limited to be constituted of only carbon atoms and hydrogen atoms(not limited to hydrocarbon groups), but is preferably a hydrocarbongroup. Further, the “hydrocarbon group” may be either saturated orunsaturated, but is preferably saturated.

As an example of the aliphatic branched, acid dissociable groups, forexample, a group represented by the formula —C(R⁷¹)(R⁷²)(R⁷³) can begiven (in the formula, each of R⁷¹ to R⁷³ independently represents alinear alkyl group of 1 to 5 carbon atoms). The group represented by theformula —C(R⁷¹)(R⁷²)(R⁷³) preferably has 4 to 8 carbon atoms, andspecific examples include a tert-butyl group, a 2-methyl-2-butyl group,a 2-methyl-2-pentyl group and a 3-methyl-3-pentyl group.

Among these, a tert-butyl group is particularly desirable.

The term “aliphatic cyclic group” refers to a monocyclic group orpolycyclic group that has no aromaticity.

The aliphatic cyclic group within the “aliphatic cyclic group-containingacid dissociable groups” may or may not have a substituent. Examples ofthe substituent include an alkyl group of 1 to 5 carbon atoms, an alkoxygroup of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl groupof 1 to 5 carbon atoms, and an oxygen atom (═O).

The basic ring of the aliphatic cyclic group exclusive of substituentsis not limited to be constituted from only carbon and hydrogen (notlimited to hydrocarbon groups), but is preferably a hydrocarbon group.Further, the hydrocarbon group may be either saturated or unsaturated,but is preferably saturated.

The aliphatic cyclic group may be monocyclic group, or a polycyclicgroup.

As such aliphatic cyclic groups, groups in which one or more hydrogenatoms have been removed from a monocycloalkane, and groups in which oneor more hydrogen atoms have been removed from a polycycloalkane such asa bicycloalkane, tricycloalkane or tetracycloalkane, which may or maynot be substituted with an alkyl group of 1 to 5 carbon atoms, afluorine atom or a fluorinated alkyl group, may be used. Specificexamples include an alicyclic hydrocarbon group such as groups in whichone or more hydrogen atoms have been removed from a monocycloalkane suchas cyclopentane and cyclohexane; and groups in which one or morehydrogen atoms have been removed from a polycycloalkane such asadamantane, norbornane, isobornane, tricyclodecane ortetracyclododecane. In these aliphatic cyclic hydrocarbon groups, partof the carbon atoms constituting the ring may be replaced with an ethergroup (—O—).

Examples of aliphatic cyclic group-containing acid dissociable groupsinclude

(i) a monovalent aliphatic cyclic group in which a substituent (a groupor an atom other than hydrogen) is bonded to the carbon atom on the ringskeleton to which an atom adjacent to the acid dissociable group (e.g.,“—O—” within “—C(═O)—O— group”) is bonded to form a tertiary carbonatom; and

(ii) a group which has a branched alkylene group containing a tertiarycarbon atom, and a monovalent aliphatic cyclic group to which thetertiary carbon atom is bonded.

In the group (i), as the substituent bonded to the carbon atom to whichan atom adjacent to the acid dissociable group on the ring skeleton ofthe aliphatic cyclic group, an alkyl group can be mentioned. Examples ofthe alkyl group include the same groups as those represented by R¹⁴ informulas (1-1) to (1-9) described later.

Specific examples of the group (i) include groups represented by generalformulas (1-1) to (1-9) shown below.

Specific examples of the group (ii) include groups represented bygeneral formulas (2-1) to (2-6) shown below.

In the formulas above, R¹⁴ represents an alkyl group; and g representsan integer of 0 to 8.

In the formulas above, each of R¹⁵ and R¹⁶ independently represents analkyl group.

In general formula (I-1) to (1-9), the alkyl group for R¹⁴ may be any oflinear, branched or cyclic, and preferably linear or branched.

The linear alkyl group preferably has 1 to 5 carbon atoms, morepreferably 1 to 4, and still more preferably 1 or 2. Specific examplesinclude a methyl group, an ethyl group, an n-propyl group, an n-butylgroup and an n-pentyl group. Among these, a methyl group, an ethyl groupor an n-butyl group is preferable, and a methyl group or an ethyl groupis more preferable.

The branched alkyl group preferably has 3 to 10 carbon atoms, and morepreferably 3 to 5. Specific examples of such branched alkyl groupsinclude an isopropyl group, an isobutyl group, a tert-butyl group, anisopentyl group and a neopentyl group, and an isopropyl group isparticularly desirable.

g is preferably an integer of 0 to 3, more preferably 1 to 3, and stillmore preferably 1 or 2.

In formulas (2-1) to (2-6), as the alkyl group for R¹⁵ and R¹⁶, the samealkyl groups as those for R¹⁴ can be used.

In formulas (1-1) to (1-9) and (2-1) to (2-6), part of the carbon atomsconstituting the ring may be replaced with an ethereal oxygen atom(—O—).

Further, in formulas (1-1) to (1-9) and (2-1) to (2-6), one or more ofthe hydrogen atoms bonded to the carbon atoms constituting the ring maybe substituted with a substituent. Examples of the substituent includean alkyl group of 1 to 5 carbon atoms, a fluorine atom and a fluorinatedalkyl group.

An “acetal-type acid dissociable group” generally substitutes a hydrogenatom at the terminal of OH-containing polar group such as a carboxygroup or hydroxyl group, so as to be bonded with an oxygen atom. Whenacid is generated upon exposure, the generated acid acts to break thebond between the acetal-type acid dissociable group and the oxygen atomto which the acetal-type, acid dissociable group is bonded, therebyforming an OH-containing polar group such as a carboxy group and ahydroxy group.

Examples of acetal-type acid dissociable groups include groupsrepresented by general formula (p1) shown below.

In the formula, R¹ and R², each independently represents a hydrogen atomor an alkyl group of 1 to 5 carbon atoms; n represents an integer of 0to 3; and Y represents an alkyl group of 1 to 5 carbon atoms or analiphatic cyclic group.

In general formula (p1) above, n is preferably an integer of 0 to 2,more preferably 0 or 1, and most preferably 0.

As the alkyl group for R¹, and R², the same alkyl groups as thosedescribed above for the alkyl groups as the substituent which may bebonded to the carbon atom on the α-position of the aforementionedα-position substituted acrylate ester can be used, although a methylgroup or ethyl group is preferable, and a methyl group is particularlydesirable.

In the present invention, it is preferable that at least one of R¹, andR², be a hydrogen atom. That is, it is preferable that the aciddissociable group (p1) be a group represented by general formula (p1-1)shown below.

In the formula, R¹, n and Y are the same as defined above.

As the alkyl group for Y, the same alkyl groups as those described abovefor the alkyl groups for the substituent which may be bonded to thecarbon atom on the α-position of the aforementioned α-positionsubstituted acrylate ester can be mentioned.

As the aliphatic cyclic group for Y, any of the aliphaticmonocyclic/polycyclic groups which have been proposed for conventionalArF resists and the like can be appropriately selected for use. Forexample, the same groups described above in connection with thealiphatic cyclic group within the “aliphatic cyclic group-containingacid dissociable groups” can be used.

As the acetal-type, acid dissociable group, groups represented bygeneral formula (p2) shown below can also be used.

In the formula, R¹⁷ and R¹⁸ each independently represents a linear orbranched alkyl group or a hydrogen atom; and R¹⁹ represents a linear,branched or cyclic alkyl group; or R¹⁷ and R¹⁹ each independentlyrepresents a linear or branched alkylene group, and the terminal of R¹⁷is bonded to the terminal of R¹⁹ to form a ring.

The alkyl group for R¹⁷ and R¹⁸ preferably has 1 to 15 carbon atoms, andmay be either linear or branched. As the alkyl group, an ethyl group ora methyl group is preferable, and a methyl group is most preferable.

It is particularly desirable that either one of R¹⁷ and R¹⁸ be ahydrogen atom, and the other be a methyl group.

R¹⁹ represents a linear, branched or cyclic alkyl group which preferablyhas 1 to 15 carbon atoms, and may be any of linear, branched or cyclic.

When R¹⁹ represents a linear or branched alkyl group, it is preferablyan alkyl group of 1 to 5 carbon atoms, more preferably an ethyl group ormethyl group, and most preferably an ethyl group.

When R¹⁹ represents a cycloalkyl group, it preferably has 4 to 15 carbonatoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10carbon atoms. As examples of the cycloalkyl group, groups in which oneor more hydrogen atoms have been removed from a monocycloalkane or apolycycloalkane such as a bicycloalkane, tricycloalkane ortetracycloalkane, which may or may not be substituted with a fluorineatom or a fluorinated alkyl group, may be used. Examples of such groupsinclude groups in which one or more hydrogen atoms have been removedfrom a monocycloalkane such as cyclopentane or cyclohexane; and groupsin which one or more hydrogen atoms have been removed from apolycycloalkane such as adamantane, norbornane, isobornane,tricyclodecane or tetracyclododecane. Among these, a group in which oneor more hydrogen atoms have been removed from adamantane is preferable.

In general formula (p2) above, R¹⁷ and R¹⁹ may each independentlyrepresent a linear or branched alkylene group (preferably an alkylenegroup of 1 to 5 carbon atoms), and the terminal of R¹⁹ may be bonded tothe terminal of R¹⁷.

In such a case, a cyclic group is formed by R¹⁷, R¹⁹, the oxygen atomhaving R¹⁹ bonded thereto, and the carbon atom having the oxygen atomand R¹⁷ bonded thereto. Such a cyclic group is preferably a 4- to7-membered ring, and more preferably a 4- to 6-membered ring. Specificexamples of the cyclic group include tetrahydropyranyl group andtetrahydrofuranyl group.

Specific examples of the structural unit (a1) include a structural unitrepresented by general formula (a1-0-1) shown below and a structuralunit represented by general formula (a1-0-2) shown below.

In the formulas, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; X¹represents an acid dissociable group; Y² represents a divalent linkinggroup; and X² represents an acid dissociable group.

In general formula (a1-0-1), as each of the alkyl group and thehalogenated alkyl group for R, the same alkyl groups and halogenatedalkyl groups as those described above for the alkyl groups and thehalogenated alkyl groups as the substituent which may be bonded to thecarbon atom on the α-position of the aforementioned α-positionsubstituted acrylate ester can be used, although R is preferably ahydrogen atom, an alkyl group of 1 to 5 carbon atoms or a fluorinatedalkyl group of 1 to 5 carbon atoms, and a hydrogen atom or a methylgroup is particularly desirable.

X¹ is not particularly limited as long as it is an acid dissociablegroup. Examples thereof include the aforementioned tertiary alkylester-type acid dissociable groups and acetal-type acid dissociablegroups, and tertiary alkyl ester-type acid dissociable groups arepreferable.

In general formula (a1-0-2), R is the same as defined above.

X² is the same as defined for X¹ in general formula (a1-0-1).

The divalent linking group for Y² is not particularly limited, andpreferable examples thereof include a divalent hydrocarbon group whichmay have a substituent and a divalent linking group containing aheteroatom.

A hydrocarbon “has a substituent” means that part or all of the hydrogenatoms within the hydrocarbon group are substituted with substituents(groups or atoms other than hydrogen atom).

The hydrocarbon group may be either an aliphatic hydrocarbon group or anaromatic hydrocarbon group.

An “aliphatic hydrocarbon group” refers to a hydrocarbon group that hasno aromaticity.

The aliphatic hydrocarbon group as the divalent hydrocarbon group for Y²may be saturated or unsaturated. In general, the aliphatic hydrocarbongroup is preferably saturated.

As specific examples of the aliphatic hydrocarbon group, a linear orbranched aliphatic hydrocarbon group, and an aliphatic hydrocarbon groupcontaining a ring in the structure thereof can be given.

The linear or branched aliphatic hydrocarbon group preferably has 1 to10 carbon atoms, more preferably 1 to 6, still more preferably 1 to 4,and most preferably 1 or 3.

As the linear aliphatic hydrocarbon group, a linear alkylene group ispreferable. Specific examples thereof include a methylene group [—CH₂—],an ethylene group [—(CH₂)₂—], a trimethylene group [—(CH₂)₃—], atetramethylene group [—(CH₂)₄—] and a pentamethylene group [—(CH₂)₅—].

As the branched aliphatic hydrocarbon group, branched alkylene groupsare preferred, and specific examples include various alkylalkylenegroups, including alkylmethylene groups such as —CH(CH₃)—, —CH(CH₂CH₃)—,—C(CH₃)₂—, —C(CH₃)(CH₂CH₃)—, —C(CH₃)(CH₂CH₂CH₃)—, and —C(CH₂CH₃)₂—;alkylethylene groups such as —CH(CH₃)CH₂—, —CH(CH₃)CH(CH₃)—,—C(CH₃)₂CH₂—, —CH(CH₂CH₃)CH₂—, and —C(CH₂CH₃)₂—CH₂—; alkyltrimethylenegroups such as —CH(CH₃)CH₂CH₂—, and —CH₂CH(CH₃)CH₂—; andalkyltetramethylene groups such as —CH(CH₃)CH₂CH₂CH₂—, and—CH₂CH(CH₃)CH₂CH₂—. As the alkyl group within the alkylalkylene group, alinear alkyl group of 1 to 5 carbon atoms is preferable.

The linear or branched aliphatic hydrocarbon group may or may not have asubstituent. Examples of the substituent include a fluorine atom, afluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O).

As examples of the hydrocarbon group containing a ring in the structurethereof, an alicyclic hydrocarbon group (a group in which two hydrogenatoms have been removed from an aliphatic hydrocarbon ring), a group inwhich the alicyclic hydrocarbon group is bonded to the terminal of thelinear or branched aliphatic hydrocarbon group and a group in which thealicyclic hydrocarbon group is interposed within the linear or branchedaliphatic hydrocarbon group, can be given. As examples of the linear orbranched aliphatic hydrocarbon group, the same groups as those describedabove can be given.

The alicyclic hydrocarbon group preferably has 3 to 20 carbon atoms, andmore preferably 3 to 12 carbon atoms.

The alicyclic hydrocarbon group may be either a monocyclic group or apolycyclic group. As the monocyclic aliphatic hydrocarbon group, a groupin which 2 hydrogen atoms have been removed from a monocycloalkane ispreferable. The monocycloalkane preferably has 3 to 6 carbon atoms, andspecific examples thereof include cyclopentane and cyclohexane. As thepolycyclic group, a group in which two hydrogen atoms have been removedfrom a polycycloalkane is preferable, and the polycyclic grouppreferably has 7 to 12 carbon atoms. Examples of the polycycloalkaneinclude adamantane, norbornane, isobornane, tricyclodecane andtetracyclododecane.

The alicyclic hydrocarbon group may or may not have a substituent.Examples of the substituent include an alkyl group of 1 to 5 carbonatoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbonatoms, and an oxygen atom (═O).

The aromatic hydrocarbon group is a hydrocarbon group having an aromaticring.

The aromatic hydrocarbon group as the divalent hydrocarbon group for Y²preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still morepreferably 5 to 20, and most preferably 6 or 15. Of these, 6 to 10carbon atoms are particularly desirable. Here, the number of carbonatoms within a substituent(s) is not included in the number of carbonatoms of the aromatic hydrocarbon group.

Specific examples of the aromatic ring within the aromatic hydrocarbongroup include an aromatic hydrocarbon ring such as benzene, biphenyl,fluorene, naphthalene, anthracene, phenanthrene, and an aromatic heteroring in which part of the carbon atoms constituting the aromatichydrocarbon ring has been substituted with a heteroatom. As examples ofthe heteroatom of the aromatic hetero ring, an oxygen atom, a sulfuratom and a nitrogen atom can be given.

Specific examples of aromatic hydrocarbon groups include a group(arylene group) which is the aromatic hydrocarbon ring having twohydrogen atom removed therefrom, and a group (for example, a group inwhich one hydrogen atom of the aryl group of an arylalkyl group such asa benzyl group, a phenethyl group, a 1-naphthylmethyl group, a2-naphthylmethyl group, a 1-naphthylethyl group or a 2-naphthylethylgroup further has been removed) in which one hydrogen atom of a group(aryl group) which is the aromatic hydrocarbon ring having one hydrogenatom removed therefrom has been substituted with an alkylene group. Thealkylene group (an alkyl chain within an arylalkyl group) preferably has1 to 4 carbon atoms, more preferably 1 or 2, and most preferably 1.

The aromatic hydrocarbon group may or may not have a substituent. Forexample, a hydrogen atom bonded to the aromatic hydrocarbon ring withinthe aromatic hydrocarbon group may be substituted with a substituent. Asthe substituent, an alkyl group, an alkoxy group, a halogen atom, ahalogenated alkyl group, a hydroxyl group, an oxygen atom (═O) or thelike can be used.

The alkyl group as the substituent is preferably an alkyl group of 1 to5 carbon atoms, and a methyl group, an ethyl group, a propyl group, ann-butyl group or a tert-butyl group is particularly desirable.

The alkoxy group as the substituent for is preferably an alkoxy grouphaving 1 to 5 carbon atoms, more preferably a methoxy group, ethoxygroup, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxygroup, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom as the substituent for the aromatichydrocarbon group include a fluorine atom, a chlorine atom, a bromineatom and an iodine atom, and a fluorine atom is preferable.

An example of the halogenated alkyl group as the substituent includes agroup in which part or all of the hydrogen atoms within theaforementioned alkyl group have been substituted with the aforementionedhalogen atoms.

With respect to a “divalent linking group containing a heteroatom”, aheteroatom is an atom other than carbon and hydrogen, and examplesthereof include an oxygen atom, a nitrogen atom, a sulfur atom and ahalogen atom.

Examples of the divalent linking group containing a heteroatom include—O—, —C(═O)—O—, —C(═O)—, —O—C(═O)—O—, —C(═O)—NH—, —NH— (H may besubstituted with a substituent such as an alkyl group or an acyl group),—S—, —S(═O)₂—, —S(═O)₂—O—, —NH—C(═O)—, ═N—, and a group represented bygeneral formula —Y²¹—O—Y²²—, —[Y²¹—C(═O)—O]_(m)—Y²²— or—Y²¹—O—C(═O)—Y²²— [in the formulas, each of Y²¹ and Y²² independentlyrepresents a divalent hydrocarbon group which may have a substituent, Orepresents an oxygen atom, and m′ represents an integer of 0 to 3].

When Y² represents —NH—, H may be substituted with a substituent such asan alkyl group, an acyl group or the like. The substituent (an alkylgroup, an acyl group or the like) preferably has 1 to 10 carbon atoms,more preferably 1 to 8, and most preferably 1 to 5.

In the group represented by the formula —Y²¹—O—Y²²—,—[Y²¹—C(═O)—O]_(m′)—Y²²— or —Y²¹—O—C(═O)—Y²²—, each of Y²¹ and Y²²independently represents a divalent hydrocarbon group which may have asubstituent. As the divalent hydrocarbon group, the same groups as thosedescribed above for the “divalent hydrocarbon group which may have asubstituent” for Y² can be mentioned.

As Y²¹, a linear aliphatic hydrocarbon group is preferable, morepreferably a linear alkylene group, still more preferably a linearalkylene group of 1 to 5 carbon atoms, and a methylene group or anethylene group is particularly desirable.

As Y²², a linear or branched aliphatic hydrocarbon group is preferable,and a methylene group, an ethylene group or an alkylmethylene group ismore preferable. The alkyl group within the alkylmethylene group ispreferably a linear alkyl group of 1 to 5 carbon atoms, more preferablya linear alkyl group of 1 to 3 carbon atoms, and most preferably amethyl group.

In the group represented by the formula —[Y²¹—C(═O)—O]_(m′)—Y²²—, m′represents an integer of 0 to 3, preferably an integer of 0 to 2, morepreferably 0 or 1, and most preferably 1. Namely, it is particularlydesirable that the group represented by the formula—[Y²¹—C(═O)—O]_(m′)—Y²²— is a group represented by the formula—Y²¹—C(═O)—O—Y²²—. Among these, a group represented by the formula—(CH₂)_(a′)—C(═O)—O—(CH₂)_(b′)— is preferable. In the formula, a′ is aninteger of 1 to 10, preferably an integer of 1 to 8, more preferably aninteger of 1 to 5, still more preferably 1 or 2, and most preferably 1.b′ is an integer of 1 to 10, preferably an integer of 1 to 8, morepreferably an integer of 1 to 5, still more preferably 1 or 2, and mostpreferably 1.

As the divalent linking group containing a heteroatom, a linear groupcontaining an oxygen atom as the heteroatom e.g., a group containing anether bond or an ester bond is preferable, and a group represented bythe aforementioned formula —Y²¹—O—Y²²—, —[Y²¹—C(═O)—O]_(m′)—Y²²— or—Y²¹—O—C(═O)—Y²²— is more preferable.

Among the above-mentioned examples, as the divalent linking group forY², a linear or branched alkylene group, a divalent alicyclichydrocarbon group or a divalent linking group containing a heteroatom isparticularly desirable. Of these, a linear or branched alkylene group ora divalent linking group containing a heteroatom is most preferable.

Specific examples of the structural unit (a1) include structural unitsrepresented by general formulas (a1-1) to (a1-4) shown below.

In the formulas, R, R¹′, R²′, n, Y and Y² are the same as defined above;and X′ represents a tertiary alkyl ester-type acid dissociable group.

Examples of the tertiary alkyl ester-type acid dissociable group for X′include the same tertiary alkyl ester-type acid dissociable groups.

As R¹′, R²′, n and Y are respectively the same as defined for R¹′, R²′,n and Y in general formula (p1) described above in connection with the“acetal-type acid dissociable group”.

As examples of Y², the same groups as those described above for Y² ingeneral formula (a1-0-2) can be given.

Specific examples of structural units represented by general formula(a1-1) to (a1-4) are shown below.

In the formulas shown below, R^(α) represents a hydrogen atom, a methylgroup or a trifluoromethyl group.

In the present invention, as the structural unit (a1), it is preferableto include at least one structural unit selected from the groupconsisting of a structural unit represented by general formula (a1-0-11)shown below, a structural unit represented by general formula (a1-0-12)shown below, a structural unit represented by general formula (a1-0-13)shown below, a structural unit represented by general formula (a1-0-14)shown below, a structural unit represented by general formula (a1-0-15)shown below and a structural unit represented by general formula(a1-0-2) shown below.

It is particularly desirable that the structural unit (a1) include atleast one member selected from the group consisting of a structural unitrepresented by general formula (a1-0-11) shown below, a structural unitrepresented by general formula (a1-0-12) shown below, a structural unitrepresented by general formula (a1-0-13) shown below, a structural unitrepresented by general formula (a1-0-14) shown below and a structuralunit represented by general formula (a1-0-15) shown below.

In the formulas, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R²¹represents an alkyl group; R²² represents a group which forms analiphatic monocyclic group with the carbon atom to which R²² is bonded;R²³ represents a branched alkyl group; R²⁴ represents a group whichforms an aliphatic polycyclic group with the carbon atom to which R²⁴ isbonded; R²⁵ represents a linear alkyl group of 1 to 5 carbon atoms; eachof R¹⁵ and R¹⁶ independently represents an alkyl group; Y² represents adivalent linking group; and X² represents an acid dissociable group.

In the formulas, R, Y² and X² are the same as defined above.

In general formula (a1-0-11), as the alkyl group for R²¹, the same alkylgroups as those described above for R¹⁴ in formulas (1-1) to (1-9) canbe used, preferably a methyl group, an ethyl group or an isopropylgroup.

As the aliphatic monocyclic group formed by R²² and the carbon atoms towhich R²² is bonded, the same aliphatic cyclic groups as those describedabove for the aforementioned tertiary alkyl ester-type acid dissociablegroup and which are monocyclic can be used. Specific examples includegroups in which one or more hydrogen atoms have been removed from amonocycloalkane. The monocycloalkane is preferably a 3- to 11-memberedring, more preferably a 3- to 8-membered ring, still more preferably a4- to 6-membered ring, and most preferably a 5- or 6-membered ring.

The monocycloalkane may or may not have part of the carbon atomsconstituting the ring replaced with an ether bond (—O—).

Further, the monocycloalkane may have a substituent such as an alkylgroup of 1 to 5 carbon atoms, a fluorine atom or a fluorinated alkylgroup of 1 to 5 carbon atoms.

As an example of R²² constituting such an aliphatic cyclic group, analkylene group which may have an ether bond (—O—) interposed between thecarbon atoms can be given.

Specific examples of structural units represented by general formula(a1-0-11) include structural units represented by the aforementionedformulas (a1-1-16) to (a1-1-23), (a1-1-27) and (a1-1-31). Among these, astructural unit represented by general formula (a1-1-02) shown belowwhich includes the structural units represented by the aforementionedformulas (a1-1-16), (a1-1-17), (a1-1-20) to (a1-1-23), (a1-1-27) and(a1-1-31) is preferable. Further, a structural unit represented bygeneral formula (a1-1-02′) shown below is also preferable.

In the formulas, h is preferably 1 or 2.

In the formulas, R and R²¹ are the same as defined above; and hrepresents an integer of 1 to 3.

In general formula (a1-0-12), as the branched alkyl group for R²³, thesame branched alkyl groups as those described above for R¹⁴ in theaforementioned formulas (1-1) to (1-9) can be used, and an isopropylgroup is particularly desirable.

As the aliphatic polycyclic group formed by R²⁴ and the carbon atoms towhich R²⁴ is bonded, the same aliphatic cyclic groups as those describedabove for the aforementioned tertiary alkyl ester-type acid dissociablegroup and which are polycyclic can be used.

Specific examples of structural units represented by general formula(a1-0-12) include structural units represented by the aforementionedformulas (a1-1-26) and (a1-1-28) to (a1-1-30).

As the structural unit (a1-0-12), a structural unit in which thealiphatic polycyclic group formed by R²⁴ and the carbon atom to whichR²⁴ is bonded is a 2-adamantyl group is preferable, and a structuralunit represented by the aforementioned formula (a1-1-26) is particularlydesirable.

In general formula (a1-0-13), R and R²⁴ are the same as defined above.

As the linear alkyl group for R²⁵, the same linear alkyl groups as thosedescribed above for R¹⁴ in the aforementioned formulas (1-1) to (1-9)can be mentioned, and a methyl group or an ethyl group is particularlydesirable.

Specific examples of structural units represented by general formula(a1-0-13) include structural units represented by the aforementionedformulas (a1-1-1) to (a1-1-2) and (a1-1-7) to (a1-1-15) which weredescribed above as specific examples of the structural unit representedby general formula (a1-1).

As the structural unit (a1-0-13), a structural unit in which thealiphatic polycyclic group formed by R²⁴ and the carbon atom to whichR²⁴ is bonded is a 2-adamantyl group is preferable, and a structuralunit represented by the aforementioned formula (a1-1-1) or (a1-1-2) isparticularly desirable.

In general formula (a1-0-14), each of R and R²² is the same as definedabove. Each of R¹⁵ and R¹⁶ is the same as defined for R¹⁵ and R¹⁶ ingeneral formulas (2-1) to (2-6).

Specific examples of structural units represented by general formula(a1-0-14) include structural units represented by the aforementionedformulas (a1-1-33) and (a1-1-34) which were described above as specificexamples of the structural unit represented by general formula (a1-1).

In general formula (a1-0-15), R and R²⁴ are the same as defined above.R¹⁵ and

R¹⁶ are the same as defined for R¹⁵ and R¹⁶ in general formulas (2-1) to(2-6).

Specific examples of structural units represented by general formula(a1-0-15) include structural units represented by the aforementionedformulas (a1-1-4) to (a1-1-6) and (a1-1-32) which were described aboveas specific examples of the structural unit represented by generalformula (a1-1).

Examples of structural units represented by general formula (a1-0-2)include structural units represented by the aforementioned formulas(a1-3) and (a1-4). The structural unit represented by formula (a1-3) isparticularly desirable.

As a structural unit represented by general formula (a1-0-2), those inwhich Y² is a group represented by the aforementioned formula—Y²¹—O—Y²²— or —Y²¹—C(═O)—O—Y²²— is particularly desirable.

Preferable examples of such structural units include a structural unitrepresented by general formula (a1-3-01) shown below, a structural unitrepresented by general formula (a1-3-02) shown below, and a structuralunit represented by general formula (a1-3-03) shown below.

In the formulas, R is the same as defined above; R¹³ represents ahydrogen atom or a methyl group; R¹⁴ represents an alkyl group; erepresents an integer of 1 to 10; and n′ represents an integer of 0 to3.

In the formula, R is as defined above; each of Y²′ and Y²″ independentlyrepresents a divalent linking group; X′ represents an acid dissociablegroup; and w represents an integer of 0 to 3.

In general formulas (a1-3-01) and (a1-3-02), R¹³ is preferably ahydrogen atom.

R¹⁴ is the same as defined for R¹⁴ in the aforementioned formulas (I-1)to (1-9).

e is preferably an integer of 1 to 8, more preferably 1 to 5, and mostpreferably 1 or 2.

n′ is preferably 1 or 2, and most preferably 2.

Specific examples of structural units represented by general formula(a1-3-01) include structural units represented by the aforementionedformulas (a1-3-25) and (a1-3-26).

Specific examples of structural units represented by general formula(a1-3-02) include structural units represented by the aforementionedformulas (a1-3-27) and (a1-3-28).

In general formula (a1-3-03), as the divalent linking group for Y²′ andY²″, the same groups as those described above for Y² in general formula(a1-3) can be used.

As Y²′, a divalent hydrocarbon group which may have a substituent ispreferable, a linear aliphatic hydrocarbon group is more preferable, anda linear alkylene group is still more preferable. Among linear alkylenegroups, a linear alkylene group of 1 to 5 carbon atoms is preferable,and a methylene group or an ethylene group is particularly desirable.

As Y²″, a divalent hydrocarbon group which may have a substituent ispreferable, a linear aliphatic hydrocarbon group is more preferable, anda linear alkylene group is still more preferable. Among linear alkylenegroups, a linear alkylene group of 1 to 5 carbon atoms is preferable,and a methylene group or an ethylene group is particularly desirable.

As the acid dissociable group for X′, the same groups as those describedabove can be used. X′ is preferably a tertiary alkyl ester-type aciddissociable group, more preferably the aforementioned group (i) in whicha substituent is bonded to the carbon atom, on the ring skeleton of themonovalent aliphatic cyclic group, to which an atom adjacent to the aciddissociable group is bonded to form a tertiary carbon atom. Among theaforementioned groups (i), a group represented by general formula (I-1)above is preferable.

w represents an integer of 0 to 3, preferably an integer of 0 to 2, morepreferably 0 or 1, and most preferably 1.

As the structural unit represented by general formula (a1-3-03), astructural unit represented by general formula (a1-3-03-1) or(a1-3-03-2) shown below is preferable, and a structural unit representedby general formula (a1-3-03-1) is particularly desirable.

In the formulas, R and R¹⁴ are the same as defined above; a′ representsan integer of 1 to 10; b′ represents an integer of 1 to 10; and trepresents an integer of 0 to 3.

In general formulas (a1-3-03-1) and (a1-3-03-2), a′ is the same asdefined above, preferably an integer of 1 to 8, more preferably 1 to 5,and most preferably 1 or 2.

b′ is the same as defined above, preferably an integer of 1 to 8, morepreferably 1 to 5, and most preferably 1 or 2.

t is preferably an integer of 1 to 3, and most preferably 1 or 2.

Specific examples of structural units represented by general formula(a1-3-03-1) or (a1-3-03-2) include structural units represented by theaforementioned formulas (a1-3-29) to (a1-3-32).

As the structural unit (a1) contained in the component (A1), 1 type ofstructural unit may be used, or 2 or more types may be used.

In the component (A1), the amount of the structural unit (a1) based onthe combined total of all structural units constituting the component(A1) is preferably 15 to 70 mol %, more preferably 15 to 60 mol %, stillmore preferably 20 to 55 mol %. When the amount of the structural unit(a1) is at least as large as the lower limit of the above-mentionedrange, a pattern can be easily formed using a resist compositionprepared from the component (A1) and also various lithography propertiessuch as sensitivity, resolution, LWR and EL are improved. Further, whenthe amount of the structural unit (a5) is no more than the upper limitof the above-mentioned range, good balance can readily be achieved withthe other structural units.

[Structural Unit (a0)]

The structural unit (a0) is a structural unit derived from an acrylateester which may have the hydrogen atom bonded to the carbon atom on theα-position substituted with a substituent and contains an —SO₂—containing cyclic group.

By virtue of the structural unit (a0) containing a —SO₂— containingcyclic group, a resist composition containing the component (A1)including the structural unit (a0) is capable of improving the adhesionof a resist film to a substrate. Further, the structural unit (a0)contributes to improvement in various lithography properties such assensitivity, resolution, exposure latitude (EL margin), LWR (line widthroughness), LER (line edge roughness) and mask reproducibility.

Here, an “—SO₂— containing cyclic group” refers to a cyclic group havinga ring containing —SO₂— within the ring structure thereof, i.e., acyclic group in which the sulfur atom (S) within —SO₂— forms part of thering skeleton of the cyclic group.

In the —SO₂— containing cyclic group, the ring containing —SO₂— withinthe ring skeleton thereof is counted as the first ring. A cyclic groupin which the only ring structure is the ring that contains —SO₂— in thering skeleton thereof is referred to as a monocyclic group, and a groupcontaining other ring structures is described as a polycyclic groupregardless of the structure of the other rings.

The —SO₂— containing cyclic group may be either a monocyclic group or apolycyclic group.

As the —SO₂— containing cyclic group, a cyclic group containing —O—SO₂—within the ring skeleton thereof, i.e., a cyclic group containing asultone ring in which —O—S— within the —O—SO₂— group forms part of thering skeleton thereof is particularly desirable.

The —SO₂— containing cyclic group preferably has 3 to 30 carbon atoms,more preferably 4 to 20, still more preferably 4 to 15, and mostpreferably 4 to 12. Herein, the number of carbon atoms refers to thenumber of carbon atoms constituting the ring skeleton, excluding thenumber of carbon atoms within a substituent.

The —SO₂— containing cyclic group may be either a —SO₂— containingaliphatic cyclic group or a —SO₂— containing aromatic cyclic group. A—SO₂— containing aliphatic cyclic group is preferable.

Examples of the —SO₂— containing aliphatic cyclic group includealiphatic cyclic groups in which part of the carbon atoms constitutingthe ring skeleton has been substituted with a —SO₂— group or a —O—SO₂—group and has at least one hydrogen atom removed from the aliphatichydrocarbon ring. Specific examples include an aliphatic hydrocarbonring in which a —CH₂— group constituting the ring skeleton thereof hasbeen substituted with a —SO₂— group and has at least one hydrogen atomremoved therefrom; and an aliphatic hydrocarbon ring in which a—CH₂—CH₂— group constituting the ring skeleton has been substituted witha —O—SO₂— group and has at least one hydrogen atom removed therefrom.

The alicyclic hydrocarbon group preferably has 3 to 20 carbon atoms, andmore preferably 3 to 12 carbon atoms.

The alicyclic hydrocarbon group may be either a monocyclic group or apolycyclic group. As the monocyclic group, a group in which two hydrogenatoms have been removed from a monocycloalkane of 3 to 6 carbon atoms ispreferable. Examples of the monocycloalkane include cyclopentane andcyclohexane. As the polycyclic group, a group in which two hydrogenatoms have been removed from a polycycloalkane of 7 to 12 carbon atomsis preferable. Examples of the polycycloalkane include adamantane,norbornane, isobornane, tricyclodecane and tetracyclododecane.

The —SO₂— containing cyclic group may have a substituent. Examples ofthe substituent include an alkyl group, an alkoxy group, a halogen atom,a halogenated alkyl group, a hydroxy group, an oxygen atom (═O), —COOR″,—OC(═O)R″ (R″ represents a hydrogen atom or an alkyl group), ahydroxyalkyl group and a cyano group.

The alkyl group for the substituent is preferably an alkyl group of 1 to6 carbon atoms. Further, the alkyl group is preferably a linear alkylgroup or a branched alkyl group. Specific examples include a methylgroup, an ethyl group, a propyl group, an isopropyl group, an n-butylgroup, an isobutyl group, a tert-butyl group, a pentyl group, anisopentyl group, a neopentyl group and a hexyl group. Among these, amethyl group or ethyl group is preferable, and a methyl group isparticularly desirable.

As the alkoxy group for the substituent, an alkoxy group of 1 to 6carbon atoms is preferable. Further, the alkoxy group is preferably alinear alkoxy group or a branched alkyl group. Specific examples of thealkoxy group include the aforementioned alkyl groups for the substituenthaving an oxygen atom (—O—) bonded thereto.

Examples of the halogen atom for the substituent include a fluorineatom, a chlorine atom, a bromine atom and an iodine atom, and a fluorineatom is preferable.

Examples of the halogenated alkyl group for the substituent includegroups in which part or all of the hydrogen atoms within theaforementioned alkyl groups have been substituted with theaforementioned halogen atoms.

As examples of the halogenated lower alkyl group for the substituent,groups in which part or all of the hydrogen atoms of the aforementionedalkyl groups for the substituent have been substituted with theaforementioned halogen atoms can be given. As the halogenated alkylgroup, a fluorinated alkyl group is preferable, and a perfluoroalkylgroup is particularly desirable.

In the —COOR″ group and the —OC(═O)R″ group, R″ is preferably a hydrogenatom or a linear, branched or cyclic alkyl group of 1 to 15 carbonatoms.

When R″ represents a linear or branched alkyl group, it is preferably analkyl group of 1 to 10 carbon atoms, more preferably an alkyl group of 1to 5 carbon atoms, and most preferably a methyl group or an ethyl group.

When R″ is a cyclic alkyl group (cycloalkyl group), it preferably has 3to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and mostpreferably 5 to 10 carbon atoms. As examples of the cycloalkyl group,groups in which one or more hydrogen atoms have been removed from amonocycloalkane or a polycycloalkane such as a bicycloalkane,tricycloalkane or tetracycloalkane, which may or may not be substitutedwith a fluorine atom or a fluorinated alkyl group, may be used. Specificexamples include groups in which one or more hydrogen atoms have beenremoved from a monocycloalkane such as cyclopentane and cyclohexane; andgroups in which one or more hydrogen atoms have been removed from apolycycloalkane such as adamantane, norbornane, isobornane,tricyclodecane or tetracyclododecane.

The hydroxyalkyl group for the substituent preferably has 1 to 6 carbonatoms, and specific examples thereof include the aforementioned alkylgroups for the substituent in which at least one hydrogen atom has beensubstituted with a hydroxy group.

More specific examples of the —SO₂— containing cyclic group includegroups represented by general formulas (3-1) to (3-4) shown below.

In the formulas, A′ represents an oxygen atom, a sulfur atom or analkylene group of 1 to 5 carbon atoms which may contain an oxygen atomor a sulfur atom; z represents an integer of 0 to 2; and R⁶ representsan alkyl group, an alkoxy group, a halogenated alkyl group, a hydroxylgroup, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group, whereinR″ represents a hydrogen atom or an alkyl group.

In general formulas (3-1) to (3-4) above, A′ represents an oxygen atom(—O—), a sulfur atom (—S—) or an alkylene group of 1 to 5 carbon atomswhich may contain an oxygen atom or a sulfur atom.

As the alkylene group of 1 to 5 carbon atoms represented by A′, a linearor branched alkylene group is preferable, and examples thereof include amethylene group, an ethylene group, an n-propylene group and anisopropylene group.

Examples of alkylene groups that contain an oxygen atom or a sulfur atominclude the aforementioned alkylene groups in which —O— or —S— is bondedto the terminal of the alkylene group or present between the carbonatoms of the alkylene group. Specific examples of such alkylene groupsinclude —O—CH₂—, —CH₂—O—CH₂—, —S—CH₂—, —CH₂—S—CH₂—.

As A′, an alkylene group of 1 to 5 carbon atoms or —O— is preferable,more preferably an alkylene group of 1 to 5 carbon atoms, and mostpreferably a methylene group.

z represents an integer of 0 to 2, and is most preferably 0.

When z is 2, the plurality of R⁶ may be the same or different from eachother.

As the alkyl group, alkoxy group, halogenated alkyl group, halogenatedalkyl group, hydroxyl group, —COOR″, —OC(═O)R″, hydroxyalkyl group andcyano group for R⁶, the same alkyl groups, alkoxy groups, halogenatedalkyl groups, halogenated alkyl groups, hydroxyl groups, —COOR″,—OC(═O)R″, hydroxyalkyl groups and cyano groups as those described aboveas the substituent which the —SO₂— containing cyclic group may have canbe used.

Specific examples of the cyclic groups represented by general formulas(3-1) to (3-4) are shown below. In the formulas shown below, “Ac”represents an acetyl group.

As the —SO₂— containing cyclic group, a group represented by theaforementioned general formula (3-1) is preferable, at least one memberselected from the group consisting of groups represented by theaforementioned chemical formulas (3-1-1), (3-1-18), (3-3-1) and (3-4-1)is more preferable, and a group represented by chemical formula (3-1-1)is most preferable.

More specific examples of the structural unit (a0) include structuralunits represented by general formula (a0-0) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R³represents a —SO₂— containing cyclic group; and R²⁹′ represents a singlebond or a divalent linking group.

In formula (a0-0), R represents a hydrogen atom, an alkyl group of 1 to5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms.

The alkyl group of 1 to 5 carbon atoms for R is preferably a linear orbranched alkyl group of 1 to 5 carbon atoms, and specific examplesthereof include a methyl group, an ethyl group, a propyl group, anisopropyl group, an n-butyl group, an isobutyl group, a tert-butylgroup, a pentyl group, an isopentyl group and a neopentyl group.

Examples of the halogenated alkyl group represented by R include a groupin which part or all of the hydrogen atoms of the aforementioned alkylgroup of 1 to 5 carbon atoms have been substituted with halogen atoms.Examples of the halogen atom include a fluorine atom, a chlorine atom, abromine atom and an iodine atom, and a fluorine atom is particularlydesirable.

As R, a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or afluorinated alkyl group of 1 to 5 carbon atoms is preferable, and ahydrogen atom or a methyl group is particularly desirable in terms ofindustrial availability.

In general formula (a0-0), R³ is the same as defined for theaforementioned —SO₂— containing group.

R²⁹′ may be either a single bond or a divalent linking group. In termsof the effects of the present invention, a divalent linking group ispreferable.

As the divalent linking group for R²⁹′, the same divalent linking groupas those described above as the divalent linking group for Y² of generalformula (a1-0-2) of the aforementioned structural unit (a1) can be used.

As the divalent linking group for R²⁹′, an alkylene group, a divalentalicyclic hydrocarbon group or a divalent linking group containing aheteroatom is preferable. Among these, an alkylene group or a divalentlinking group containing an ester bond (—C(═O)—O—) is preferable.

As the alkylene group, a linear or branched alkylene group ispreferable. Specific examples include the same linear alkylene groupsand branched alkylene groups as those described above for the aliphatichydrocarbon group represented by Y².

As the divalent linking group containing an ester bond, a grouprepresented by general formula: —R²—C(═O)—O— (in the formula, R²represents a divalent linking group) is particularly desirable. That is,the structural unit (a0) is preferably a structural unit represented bygeneral formula (a0-O-1) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R²represents a divalent linking group; and R³ represents a —SO₂—containing cyclic group.

R² is not particularly limited. For example, the same divalent linkinggroups as those described for R²⁹′ in general formula (a0-0) can bementioned.

As the divalent linking group for R², an alkylene group, a divalentalicyclic hydrocarbon group or a divalent linking group containing aheteroatom is preferable.

As the linear or branched alkylene group, the divalent alicyclichydrocarbon group and the divalent linking group containing aheteroatom, the same linear or branched alkylene group, divalentalicyclic hydrocarbon group and divalent linking group containing aheteroatom as those described above as preferable examples of R²⁹′ canbe mentioned.

Among these, a linear or branched alkylene group, or a divalent linkinggroup containing an oxygen atom as a heteroatom is more preferable.

As the linear alkylene group, a methylene group or an ethylene group ispreferable, and a methylene group is particularly desirable.

As the branched alkylene group, an alkylmethylene group or analkylethylene group is preferable, and —CH(CH₃)—, —C(CH₃)₂— or—C(CH₃)₂CH₂— is particularly desirable.

As the divalent linking group containing a heteroatom, a divalentlinking group containing an ether bond or an ester bond is preferable,and a group represented by the aforementioned formula —Y²¹—O—Y²²—,formula —[Y²¹—C(═O)—O]_(m′)—Y²²— or formula —Y²¹—O—C(═O)—Y²²— is morepreferable. Each of Y²¹, Y²², and m′ is the same as defined above.

Among these, a group represented by the formula —Y²¹—O—C(═O)—Y²²— ispreferable, and a group represented by the formula:—(CH₂)_(c)—O—C(═O)—(CH₂)_(d)— is particularly desirable. c represents aninteger of 1 to 5, preferably an integer of 1 to 3, and more preferably1 or 2. d represents an integer of 1 to 5, preferably an integer of 1 to3 and more preferably 1 or 2.

In particular, as the structural unit (a0), a structural unitrepresented by general formula (a0-0-11) or (a0-0-12) shown below ispreferable, and a structural unit represented by general formula(a0-0-12) shown below is more preferable.

In the formulas, R, A′, R⁶, z and R² are the same as defined above.

In general formula (a0-O-11), A′ is preferably a methylene group, anethylene group, an oxygen atom (—O—) or a sulfur atom (—S—).

As R², a linear or branched alkylene group or a divalent linking groupcontaining an oxygen atom is preferable. As the linear or branchedalkylene group and the divalent linking group containing an oxygen atomrepresented by R², the same linear or branched alkylene groups and thedivalent linking groups containing an oxygen atom as those describedabove can be mentioned.

As the structural unit represented by general formula (a0-0-12), astructural unit represented by general formula (a0-0-12a) or (a0-0-12b)shown below is particularly desirable.

In the formulas, R and A′ are the same as defined above; and each of cand d is the same as defined above; f represents an integer of 1 to 5(preferably an integer of 1 to 3).

As the structural unit (a0) contained in the component (A1), 1 type ofstructural unit may be used, or 2 or more types may be used.

Since the shape of the resist pattern formed using a resist compositioncontaining the component (A1) including the structural unit (a0) isexcellent and various lithography properties such as EL margin, LWR andmask reproducibility are excellent, in the component (A1), the amount ofthe structural unit (a0) based on the combined total of all structuralunits constituting the component (A1) is preferably 1 to 60 mol %, morepreferably 5 to 55 mol %, still more preferably 10 to 50 mol %, and mostpreferably 15 to 45 mol %.

[Structural Unit (a2)]

The structural unit (a2) represents a structural unit derived from anacrylate ester which may have the hydrogen atom bonded to the carbonatom on the α-position substituted with a substituent and contains alactone-containing cyclic group.

The term “lactone-containing cyclic group” refers to a cyclic groupincluding one ring containing a —O—C(═O)— structure (lactone ring). Theterm “lactone ring” refers to a single ring containing a —O—C(═O)—structure, and this ring is counted as the first ring. Alactone-containing cyclic group in which the only ring structure is thelactone ring is referred to as a monocyclic group, and groups containingother ring structures are described as polycyclic groups regardless ofthe structure of the other rings.

When the component (A1) is used for forming a resist film, thelactone-containing cyclic group of the structural unit (a2) is effectivein improving the adhesion between the resist film and the substrate, andincreasing the compatibility with the developing solution (particularly,in the case of an alkali developing process) containing water.

As the structural unit (a2), there is no particular limitation, and anarbitrary structural unit may be used.

Specific examples of lactone-containing monocyclic groups include agroup in which one hydrogen atom has been removed from a 4- to6-membered lactone ring, such as a group in which one hydrogen atom hasbeen removed from β-propiolatone, a group in which one hydrogen atom hasbeen removed from γ-butyrolactone, and a group in which one hydrogenatom has been removed from δ-valerolactone. Further, specific examplesof lactone-containing polycyclic groups include groups in which onehydrogen atom has been removed from a lactone ring-containingbicycloalkane, tricycloalkane or tetracycloalkane.

More specifically, examples of the structural unit (a2) includestructural units represented by general formulas (a2-1) to (a2-5) shownbelow.

In the formulas, R represents a hydrogen atom, a lower alkyl group or ahalogenated lower alkyl group; each R′ independently represents ahydrogen atom, an alkyl group of 1 to 5 carbon atoms, an alkoxy group of1 to 5 carbon atoms or —COOR″, wherein R″ represents a hydrogen atom oran alkyl group; R²⁹ represents a single bond or a divalent linkinggroup; s″ represents an integer of 0 or 1 to 2; A″ represents an oxygenatom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms whichmay contain an oxygen atom or a sulfur atom; and m represents an integerof 0 or 1.

In general formulas (a2-1) to (a2-5), R is the same as defined for R inthe structural unit (a1).

Examples of the alkyl group of 1 to 5 carbon atoms for R′ include amethyl group, an ethyl group, a propyl group, an n-butyl group and atert-butyl group.

Examples of the alkoxy group of 1 to 5 carbon atoms for R′ include amethoxy group, an ethoxy group, an n-propoxy group, an iso-propoxygroup, an n-butoxy group and a tert-butoxy group

In terms of industrial availability, R′ is preferably a hydrogen atom.

R″ is preferably a hydrogen atom, or linear, branched or cyclic alkylgroup of 1 to 15 carbon atoms.

When R″ is a linear or branched alkyl group, it preferably has 1 to 10carbon atoms, more preferably 1 to 5 carbon atoms.

When R″ is a cyclic alkyl group (cycloalkyl group), it preferably has 3to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and mostpreferably 5 to 10 carbon atoms. As examples of the cycloalkyl group,groups in which one or more hydrogen atoms have been removed from amonocycloalkane or a polycycloalkane such as a bicycloalkane,tricycloalkane or tetracycloalkane, which may or may not be substitutedwith a fluorine atom or a fluorinated alkyl group, may be used. Examplesof such groups include groups in which one or more hydrogen atoms havebeen removed from a monocycloalkane such as cyclopentane or cyclohexane;and groups in which one or more hydrogen atoms have been removed from apolycycloalkane such as adamantane, norbornane, isobornane,tricyclodecane or tetracyclododecane.

A″ is preferably an alkylene group of 1 to 5 carbon atoms or an —O—, andmore preferably an alkylene group of 1 to 5 carbon atoms, and amethylene group is particularly desirable.

R²⁹ represents a single bond or a divalent linking group. The divalentlinking group is the same divalent linking groups as those describedabove for Y² in the aforementioned formula (a1-0-2). Among these, analkylene group, an ester bond (—C(═O)—O—) or a combination of these ispreferable. The alkylene group as a divalent linking group for R²⁹ ispreferably a linear or branched alkylene group. Specific examplesinclude the same linear alkylene groups and branched alkylene groups asthose described above for the aliphatic hydrocarbon group represented byY².

s″ is preferably an integer of 1 or 2.

Specific examples of structural units represented by general formulas(a2-1) to (a2-5) are shown below.

In the formulas shown below, R^(α) represents a hydrogen atom, a methylgroup or a trifluoromethyl group.

As the structural unit (a2) contained in the component (A1), 1 type ofstructural unit may be used, or 2 or more types may be used.

The structural unit (a2) is preferably at least one selected from thegroup consisting of structural units represented by the aforementionedgeneral formulas (a2-1) to (a2-5), and more preferably at least oneselected from the group consisting of structural units represented bygeneral formulas (a2-1) to (a2-3). Of these, at least one selected fromthe group consisting of structural units represented by chemicalformulas (a2-1-1), (a2-1-2), (a2-2-1), (a2-2-7), (a2-3-1) and (a2-3-5)is particularly desirable.

In the component (A1), the amount of the structural unit (a2) based onthe combined total of all structural units constituting the component(A1) is preferably 5 to 60 mol %, more preferably 10 to 50 mol %, andstill more preferably 10 to 45 mol %. When the amount of the structuralunit (a2) is at least as large as the lower limit of the above-mentionedrange, the effect of using the structural unit (a2) can besatisfactorily achieved. On the other hand, when the amount of thestructural unit (a2) is no more than the upper limit of theabove-mentioned range, a good balance can readily be achieved with theother structural units.

[Structural Unit (a3)]

The structural unit (a3) represents a structural unit derived from anacrylate ester which may have the hydrogen atom bonded to the carbonatom on the α-position substituted with a substituent and contains apolar group-containing aliphatic hydrocarbon group (provided that theaforementioned structural units are excluded).

When the component (A1) includes the structural unit (a3), thehydrophilicity of the component (A1) is enhanced, thereby contributingto improvement in resolution.

Examples of the polar group include a hydroxyl group, cyano group,carboxyl group, or hydroxyalkyl group in which some of the hydrogenatoms of the alkyl group have been substituted with fluorine atoms,although a hydroxyl group is particularly desirable.

Examples of the aliphatic hydrocarbon group include linear or branchedhydrocarbon groups (preferably alkylene groups) of 1 to 10 carbon atoms,and cyclic aliphatic hydrocarbon groups (cyclic groups). The cyclicgroups may be a monocyclic group or a polycyclic group. These cyclicgroups can be selected appropriately from the multitude of groups thathave been proposed for the resins of resist compositions designed foruse with ArF excimer lasers. The cyclic groups are preferably thepolycyclic group, and more preferably have 7 to 30 carbon atoms.

Of the various possibilities, structural units derived from an acrylateester that include an aliphatic polycyclic group that contains ahydroxyl group, cyano group, carboxyl group or a hydroxyalkyl group inwhich part of the hydrogen atoms of the alkyl group have beensubstituted with fluorine atoms are particularly desirable. Examples ofthe polycyclic group include groups in which two or more hydrogen atomshave been removed from a bicycloalkane, tricycloalkane, tetracycloalkaneor the like. Specific examples include groups in which two or morehydrogen atoms have been removed from a polycycloalkane such asadamantane, norbornane, isobornane, tricyclodecane ortetracyclododecane. Of these polycyclic groups, groups in which two ormore hydrogen atoms have been removed from adamantane, norbornane ortetracyclododecane are preferred industrially.

When the aliphatic hydrocarbon group within the polar group-containingaliphatic hydrocarbon group is a linear or branched hydrocarbon group of1 to 10 carbon atoms, the structural unit (a3) is preferably astructural unit derived from a hydroxyethyl ester of acrylic acid. Onthe other hand, when the hydrocarbon group is a polycyclic group,structural units represented by formulas (a3-1), (a3-2) and (a3-3) shownbelow are preferable.

In the formulas, R is the same as defined above; j is an integer of 1 to3; k is an integer of 1 to 3; t′ is an integer of 1 to 3; 1 is aninteger of 1 to 5; and s is an integer of 1 to 3.

In general formula (a3-1), j is preferably 1 or 2, and morepreferably 1. When j is 2, it is preferable that the hydroxyl groups bebonded to the 3rd and 5th positions of the adamantyl group. When j is 1,it is preferable that the hydroxyl group be bonded to the 3rd positionof the adamantyl group.

j is preferably 1, and it is particularly desirable that the hydroxylgroup be bonded to the 3rd position of the adamantyl group.

In formula (a3-2), k is preferably 1. The cyano group is preferablybonded to the 5th or 6th position of the norbornyl group.

In formula (a3-3), t′ is preferably 1. l is preferably 1. s ispreferably 1. Further, it is preferable that a 2-norbornyl group or3-norbornyl group be bonded to the terminal of the carboxy group of theacrylic acid. The fluorinated alkylalcohol is preferably bonded to the5th or 6th position of the norbornyl group.

As the structural unit (a3) contained in the component (A1), one type ofstructural unit may be used, or two or more types may be used incombination.

In the component (A1), the amount of the structural unit (a3) based onthe combined total of all structural units constituting the component(A1) is preferably 5 to 50 mol %, more preferably 5 to 40 mol %, andstill more preferably 5 to 25 mol %. When the amount of the structuralunit (a3) is at least as large as the lower limit of the above-mentionedrange, the effect of using the structural unit (a3) can besatisfactorily achieved. On the other hand, when the amount of thestructural unit (a3) is no more than the upper limit of theabove-mentioned range, a good balance is readily achieved with the otherstructural units.

[Other Structural Units]

The component (A1) may also have a structural unit other than theabove-mentioned structural units (a5), structural units (a1), structuralunits (a0), structural units (a2) and structural units (a3), as long asthe effects of the present invention are not impaired.

As such another structural unit, any structural unit which cannot beclassified as one of the above structural units can be used without anyparticular limitation, and any of the multitude of conventionalstructural units used within resist resins for ArF excimer lasers or KrFexcimer lasers (and particularly for ArF excimer lasers) can be used.

As examples of such another structural unit, a structural unit (a4)derived from an acrylate ester which may have the hydrogen atom bondedto the carbon atom on the α-position substituted with a substituent andcontains an acid non-dissociable, aliphatic polycyclic group.

(Structural Unit (a4))

The structural unit (a4) represents a structural unit derived from anacrylate ester which may have the hydrogen atom bonded to the carbonatom on the α-position substituted with a substituent and contains anacid non-dissociable, aliphatic polycyclic group.

With respect to the structural unit (a4), examples of this polycyclicgroup include the same polycyclic groups as those described above inrelation to the aforementioned structural unit (a1), and any of themultitude of conventional polycyclic groups used within the resincomponent of resist compositions for ArF excimer lasers or KrF excimerlasers (and particularly for ArF excimer lasers) can be used.

In consideration of industrial availability and the like, at least onepolycyclic group selected from amongst a tricyclodecyl group, adamantylgroup, tetracyclododecyl group, isobornyl group, and norbornyl group isparticularly desirable. These polycyclic groups may be substituted witha linear or branched alkyl group of 1 to 5 carbon atoms.

Specific examples of the structural unit (a4) include units withstructures represented by general formulas (a-4-1) to (a-4-5) shownbelow.

In the formulas, R is the same as defined above.

When such a structural unit (a4) is included in the component (A1), theamount of the structural unit (a4) based on the combined total of allthe structural units that constitute the component (A1) is preferablywithin the range from 1 to 30 mol %, and more preferably from 10 to 20mol %.

In the resist composition of the present invention, the component (A)contains a polymeric compound (A1) having a structural unit (a5).

Preferable examples of the component (A1) include a polymeric compoundhaving structural units (a5) and (a1).

Specific examples of the component (A1) include a polymeric compoundconsisting of the structural units (a5) and (a1), a polymeric compoundconsisting of the structural units (a5), (a1) and (a0), a polymericcompound consisting of the structural units (a5), (a1) and (a3), and apolymeric compound consisting of the structural units (a5), (a1), (a2)and (a3).

In the component (A), as the component (A1), one type of structural unitmay be used, or two or more types may be used in combination.

When two or more types of component (A1) are used in combination, thecombined total amount of the structural unit (a5) in the two or moretypes of component (A1) based on the combined total of all thestructural units that constitute two or more types of component (A1) ispreferably 5 to 50 mol %, more preferably 7 to 45 mol %, still morepreferably 10 to 40 mol %, and most preferably 20 to 40 mol %.

When the combined total amount of the structural unit (a5) is at leastas large as the lower limit of the above-mentioned range, diffusion ofacid generated upon exposure can readily be controlled using a resistcomposition prepared from the component (A1), and lithography propertiessuch as EL, LWR are improved. On the other hand, when the combined totalamount of the structural unit (a5) is no more than the upper limit ofthe above-mentioned range, good balance can readily be achieved with theother structural units.

The weight average molecular weight (Mw) (the polystyrene equivalentvalue determined by gel permeation chromatography (GPC)) of thecomponent (A1) is not particularly limited, but is preferably 1,000 to50,000, more preferably 1,500 to 30,000, and most preferably 2,000 to20,000. When the weight average molecular weight is no more than theupper limit of the above-mentioned range, the resist compositionexhibits a satisfactory solubility in a resist solvent. On the otherhand, when the weight average molecular weight is at least as large asthe lower limit of the above-mentioned range, dry etching resistance andthe cross-sectional shape of the resist pattern become satisfactory.

Further, the dispersity (Mw/Mn) of the component (A1) is notparticularly limited, but is preferably 1.0 to 5.0, more preferably 1.0to 3.0, and most preferably 1.0 to 2.5.

The component (A1) can be obtained, for example, by a conventionalradical polymerization or the like of the monomers corresponding witheach of the structural units, using a radical polymerization initiatorsuch as azobisisobutyronitrile (AIBN).

Furthermore, in the component (A1), by using a chain transfer agent suchas HS—CH₂—CH₂—CH₂—C(CF₃)₂—OH, a —C(CF₃)₂—OH group can be introduced atthe terminals of the component (A1). Such a copolymer having introduceda hydroxyalkyl group in which some of the hydrogen atoms of the alkylgroup are substituted with fluorine atoms is effective in reducingdeveloping defects and LER (line edge roughness: unevenness of the sidewalls of a line pattern).

As the monomers for deriving the corresponding structural units,commercially available monomers may be used, or the monomers may besynthesized by a conventional method.

In the resist composition of the present invention, the component (A)may be used in combination with a base component which exhibitsincreased polarity under action of acid other than the component (A1).

The base component other than the component (A1) is not particularlylimited, and any of the multitude of conventional base components usedwithin chemically amplified resist compositions such as a polymericcompound having the aforementioned structural unit (a1) as an essentialcomponent, and optionally structural units (a2) to (a4) or (a0), a baseresin such as novolak resins and Polyhydroxystyrene (PHS)-based resins,and a low molecular weight compound component can be appropriatelyselected for use.

Examples of the low molecular weight compound component include a lowmolecular weight compound having a molecular weight of 500 to less than4,000 and having an acid dissociable group described above in connectionwith the component (A1) and a hydrophilic group. Specific examples ofthe low molecular weight compound include compounds containing aplurality of phenol skeletons in which a part of the hydrogen atomswithin hydroxyl groups have been substituted with the aforementionedacid dissociable groups.

In the component (A), the amount of the component (A1) based on thetotal weight of the component (A) is preferably 25% by weight or more,more preferably 50% by weight or more, still more preferably 75% byweight or more, and may be even 100% by weight. When the amount of thecomponent (A1) is 25% by weight or more, a resist pattern which exhibitshigher resolution and higher rectangularity can be readily formed.

In the resist composition of the present invention, the amount of thecomponent (A) can be appropriately adjusted depending on the thicknessof the resist film to be formed, and the like.

<Component (B)>

In the resist composition of the present invention, as the component(B), there is no particular limitation, and any of the known acidgenerators used in conventional chemically amplified resist compositionscan be used.

Examples of these acid generators are numerous, and include onium saltacid generators such as iodonium salts and sulfonium salts; oximesulfonate acid generators; diazomethane acid generators such as bisalkylor bisaryl sulfonyl diazomethanes and poly(bis-sulfonyl)diazomethanes;nitrobenzylsulfonate acid generators; iminosulfonate acid generators;and disulfone acid generators.

As an onium salt acid generator, a compound represented by generalformula (b-1) or (b-2) shown below can be used.

In the formulas above, R¹″ to R³″, R⁵″ and R⁶″ each independentlyrepresents an aryl group, alkyl group or alkenyl group which may have asubstituent, wherein two of R¹″ to R³″ may be bonded to each other toform a ring with the sulfur atom; and R⁴″ represents an alkyl group, ahalogenated alkyl group, an aryl group or an alkenyl group which mayhave a substituent.

In formula (b-1), R¹″ to R³″ each independently represents an aryl groupwhich may have a substituent, an alkyl group which may have asubstituent, and an alkenyl group which may have a substituent. Two ofR¹″ to R³″ may be bonded to each other to form a ring with the sulfuratom.

Further, since lithography properties and the shape of the resistpattern are improved, among R¹″ to R³″, at least one is preferably anaryl group, two or more groups are more preferably aryl groups, and itis particularly desirable that all of R¹″ to R³″ be aryl groups.

As examples of the aryl group of R¹″ to R³″, an unsubstituted aryl groupof 6 to 20 carbon atoms and a substituted aryl group in which part orall of the hydrogen atoms within the unsubstituted aryl group have beensubstituted with an alkyl group, an alkoxy group, a halogen atom, ahydroxyl group, an oxo group (═O), an aryl group, an alkoxyalkyloxygroup, an alkoxycarbonylalkyloxy group, —C(═O)—O—R⁶′, —O—C(═O)—R⁷′, and—O—R⁸′ can be given. Each of R⁶′, R⁷′ and R⁸′ represents a linear orbranched saturated hydrocarbon group of 1 to 25 carbon atoms or a cyclicsaturated hydrocarbon group of 3 to 20 carbon atoms, or a linear orbranched aliphatic unsaturated hydrocarbon group of 2 to 5 carbon atoms.

With respect to R¹″ to R³″, the unsubstituted aryl group is preferablyan aryl group having 6 to 10 carbon atoms because it can be synthesizedat a low cost. Specific examples thereof include a phenyl group and anaphthyl group.

The alkyl group as the substituent of the substituted aryl group for R¹″to R³″ is preferably an alkyl group having 1 to 5 carbon atoms, and mostpreferably a methyl group, an ethyl group, a propyl group, an n-butylgroup, or a tert-butyl group.

The alkoxy group for the substituent of the substituted aryl group ispreferably an alkoxy group having 1 to 5 carbon atoms, most preferably amethoxy group, an ethoxy group, an n-propoxy group, an iso-propoxygroup, an n-butoxy group or a tert-butoxy group.

The halogen atom for the substituent of the substituted aryl group ispreferably a fluorine atom.

As examples of the aryl group for the substituent of the substitutedaryl group, the same groups as those described above for the aryl groupin R¹″ to R³″ can be given, preferably an aryl group of 6 to 20 carbonatoms, more preferably an aryl group of 6 to 10 carbon atoms, and stillmore preferably a phenyl group and a naphthyl group.

Examples of the alkoxyalkyloxy group of the substituted aryl groupinclude a group represented by general formula —O—C(R⁴⁷)(R⁴⁸)—O—R⁴⁹ (inthe formula, each of R⁴⁷ and R⁴⁸ independently represents a hydrogenatom or a linear or branched alkyl group, and R⁴⁹ represents an alkylgroup.

The alkyl group for R⁴⁷ and R⁴⁸ preferably has 1 to 5 carbon atoms, andmay be either linear or branched. As the alkyl group, an ethyl group ora methyl group is preferable, and a methyl group is most preferable.

It is preferable that at least one of R⁴⁷ and R⁴⁸ represent a hydrogenatom. It is particularly desirable that at least one of R⁴⁷ and R⁴⁸represent a hydrogen atom, and the other represent a hydrogen atom or amethyl group.

The alkyl group for R⁴⁹ preferably has 1 to 15 carbon atoms, and may belinear, branched or cyclic.

The linear or branched alkyl group for R⁴⁹ preferably has 1 to 5 carbonatoms. Examples thereof include a methyl group, an ethyl group, a propylgroup, an n-butyl group and a tert-butyl group.

The cyclic alkyl group for R⁴⁹ preferably has 4 to 15 carbon atoms, morepreferably 4 to 12, and most preferably 5 to 10. Specific examplesthereof include groups in which one or more hydrogen atoms have beenremoved from a monocycloalkane or a polycycloalkane such as abicycloalkane, tricycloalkane or tetracycloalkane, and which may or maynot be substituted with an alkyl group of 1 to 5 carbon atoms, afluorine atom or a fluorinated alkyl group. Examples of themonocycloalkane include cyclopentane and cyclohexane. Examples ofpolycycloalkanes include adamantane, norbornane, isobornane,tricyclodecane and tetracyclododecane. Among these, a group in which oneor more hydrogen atoms have been removed from adamantane is preferable.

Examples of the alkoxycarbonylalkyloxy group of the substituted arylgroup include a group represented by general formula —O—R⁵⁰—C(═O)—O—R⁵⁶(in the formula, R⁵⁰ represents a linear or branched alkylene group, andR⁵⁶ represents a tertiary alkyl group.

The linear or branched alkylene group for R⁵⁰ preferably has 1 to 5carbon atoms. Examples thereof include a methylene group, an ethylenegroup, a trimethylene group, a tetramethylene group and a1,1-dimethylethylene group.

As examples of the tertiary alkyl group for R⁵⁶, a 2-methyl-2-adamantylgroup, a 2-ethyl-2-adamantyl group, a 1-methyl-1-cyclopentyl group, a1-ethyl-1-cyclopentyl group, a 1-methyl-1-cyclohexyl group, a1-ethyl-1-cyclohexyl group, a 1-(1-adamantyl)-1-methylethyl group, a1-(1-adamantyl)-1-methylpropyl group, a 1-(1-adamantyl)-1-methylbutylgroup, a 1-(1-adamantyl)-1-methylpentyl group, a1-(1-cyclopentyl)-1-methylethyl group, a1-(1-cyclopentyl)-1-methylpropyl group, a1-(1-cyclopentyl)-1-methylbutyl group, a1-(1-cyclopentyl)-1-methylpentyl group, a 1-(1-cyclohexyl)-1-methylethylgroup, a 1-(1-cyclohexyl)-1-methylpropyl group, a1-(1-cyclohexyl)-1-methylbutyl group, a 1-(1-cyclohexyl)-1-methylpentylgroup, a tert-butyl group, a tert-pentyl group, and a tert-hexyl groupcan be given.

Further, examples include a group in which R⁵⁶ of the aforementionedgeneral formula —O—R⁵⁰—C(═O)—O—R⁵⁶ is replaced by R⁵⁶′. R⁵⁶′ representsan aliphatic cyclic group which may contain a hydrogen atom, an alkylgroup, a fluorinated alkyl group or a heteroatom.

As examples of the alkyl group for R⁵⁶′, the same alkyl groups as thosedescribed above for R⁴⁹ can be given.

As the fluorinated alkyl group for R⁵⁶′, the aforementioned alkyl groupfor R⁴⁹ in which part or all of the hydrogen atoms have been substitutedwith fluorine atoms can be used.

As the aliphatic cyclic group which may contain a heteroatom for R⁵⁶′,an aliphatic cyclic group having no heteroatom, an aliphatic cyclicgroup containing a heteroatom in the ring structure, an aliphatic cyclicgroup in which a hydrogen atom thereof has been substituted with aheteroatom can be given.

Examples of the aliphatic cyclic group having no heteroatom for R⁵⁶′include groups in which one or more hydrogen atoms have been removedfrom a monocycloalkane or a polycycloalkane such as a bicycloalkane, atricycloalkane or a tetracycloalkane. Examples of the monocycloalkaneinclude cyclopentane and cyclohexane. Examples of polycycloalkanesinclude adamantane, norbornane, isobornane, tricyclodecane andtetracyclododecane. Among these, a group in which one or more hydrogenatoms have been removed from adamantane is preferable.

Specific examples of the aliphatic cyclic group containing a heteroatomin the ring structure for R⁵⁶′ include a group represented bybelow-described formulas (L1) to (L6) or (S1) to (S4).

Specific examples of the aliphatic cyclic group in which a hydrogen atomthereof has been substituted with a heteroatom for R⁵⁶′ include analiphatic cyclic group in which a hydrogen atom thereof has beensubstituted with an oxygen atom (═O).

In formula —C(═O)—O—R⁶′, —O—C(═O)—R⁷′ or —O—R⁸′, each of R⁶′, R⁷′ andR⁸′ represents a linear or branched saturated hydrocarbon group of 1 to25 carbon atoms or a cyclic saturated hydrocarbon group of 3 to 20carbon atoms, or a linear or branched aliphatic unsaturated hydrocarbongroup of 2 to 5 carbon atoms.

The linear or branched saturated hydrocarbon group has 1 to 25 carbonatoms, preferably 1 to 15 carbon atoms, and more preferably 4 to 10carbon atoms.

As examples of the linear saturated hydrocarbon group, a methyl group,an ethyl group, a propyl group, a butyl group, a pentyl group, a hexylgroup, a heptyl group, an octyl group, a nonyl group and a decyl groupcan be used.

As examples of the branched saturated hydrocarbon group, the tertiaryalkyl group for R⁵⁶, a 1-methylethyl group, a 1-methylpropyl group, a2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group anda 4-methylpentyl group can be given.

The linear or branched saturated hydrocarbon group may have asubstituent. Examples of the substituent include an alkoxy group, ahalogen atom, a halogenated alkyl group, a hydroxy group, an oxygen atom(═O), a cyano group and a carboxy group.

The alkoxy group as the substituent for the linear or branched saturatedhydrocarbon group is preferably an alkoxy group having 1 to 5 carbonatoms, more preferably a methoxy group, ethoxy group, n-propoxy group,iso-propoxy group, n-butoxy group or tert-butoxy group, and mostpreferably a methoxy group or an ethoxy group.

Examples of the halogen atom as the substituent for the linear orbranched saturated hydrocarbon group include a fluorine atom, a chlorineatom, a bromine atom and an iodine atom, and a fluorine atom ispreferable.

An example of the halogenated alkyl group as the substituent for thelinear or branched saturated hydrocarbon group includes a group in whichpart or all of the hydrogen atoms within the aforementioned linear orbranched saturated hydrocarbon group have been substituted with theaforementioned halogen atoms.

The cyclic saturated hydrocarbon group of 3 to 20 carbon atoms for R⁶′,R⁷′ and R⁸′ may be either a monocyclic group or a polycyclic group. Asthe aliphatic cyclic group, a group in which one hydrogen atom has beenremoved from a monocycloalkane or a polycycloalkane such as abicycloalkane, tricycloalkane or tetracycloalkane can be used. Specificexamples include groups in which one hydrogen atom has been removed froma monocycloalkane such as cyclopentane, cyclohexane, cycloheptane orcyclooctane; and groups in which one hydrogen atom has been removed froma polycycloalkane such as adamantane, norbornane, isobornane,tricyclodecane or tetracyclododecane.

The cyclic saturated hydrocarbon group may have a substituent. Forexample, part of the carbon atoms constituting the ring within thecyclic alkyl group may be substituted with a heteroatom, or a hydrogenatom bonded to the ring within the cyclic alkyl group may be substitutedwith a substituent.

In the former example, groups in which one or more hydrogen atoms havebeen removed from a heterocycloalkane in which part of the carbon atomsconstituting the ring within the aforementioned monocycloalkane orpolycycloalkane has been substituted with a heteroatom such as an oxygenatom, a sulfur atom or a nitrogen atom can be used. Further, the cyclicsaturated hydrocarbon group may have an ester bond (—C(═O)—O—) in thering structure. Specific examples thereof include lactone-containingmonocyclic groups such as a group in which one hydrogen atom has beenremoved from γ-butyrolactone, and lactone-containing polycyclic groupssuch as groups in which one hydrogen atom has been removed from alactone ring-containing bicycloalkane, tricycloalkane ortetracycloalkane.

In the latter example, as the substituent, the same as theabove-mentioned substituents which the linear or branched alkyl groupmay have, lower alkyl groups or the like can be used.

Further, R⁶′, R⁷′ and R⁸′ may be a combination of a linear or branchedalkyl group and a cyclic alkyl group.

As examples of a combination of the linear or branched alkyl group andthe cyclic alkyl group, a group in which a cyclic alkyl group as asubstituent is bonded to a linear or branched alkyl group, and a groupin which a linear or branched alkyl group as a substituent is bonded toa cyclic alkyl group can be used.

As examples of the linear aliphatic unsaturated hydrocarbon groups forR⁶′, R⁷′, and R⁸′, a vinyl group, a propenyl group (an allyl group) anda butynyl group can be given.

Examples of branched aliphatic unsaturated hydrocarbon groups for R⁶′,R⁷′ and R⁸′ include a 1-methylpropenyl group and a 2-methylpropenylgroup.

The linear or branched aliphatic unsaturated hydrocarbon group may havea substituent. As the substituent, the same as the above-mentionedsubstituents which the linear or branched alkyl group may have can beused.

With respect to R⁷′ and R⁸′, among the above-mentioned examples, alinear or branched saturated hydrocarbon group of 1 to 15 carbon atoms,or a cyclic saturated hydrocarbon group of 3 to 20 carbon atoms ispreferable, since lithography properties and the shape of the resistpattern are excellent.

It is preferable that the aryl group for each of R¹″ to R³″ represent aphenyl group or a naphthyl group.

The alkyl group for R¹″ to R³″ includes, for example, a linear, branchedor cyclic alkyl group having 1 to 10 carbon atoms. Among these, in termsof achieving excellent resolution, the alkyl group preferably has 1 to 5carbon atoms. Specific examples thereof include a methyl group, an ethylgroup, an n-propyl group, an isopropyl group, an n-butyl group, anisobutyl group, an n-pentyl group, a cyclopentyl group, a hexyl group, acyclohexyl group, a nonyl group, and a decyl group, and a methyl groupis most preferable because it is excellent in resolution and can besynthesized at a low cost.

The alkenyl group for R¹″ to R³″ preferably has 2 to 10 carbon atoms,more preferably 2 to 5 carbon atoms, and still more preferably 2 to 4.Specific examples thereof include a vinyl group, a propenyl group (anallyl group), a butynyl group, a 1-methylpropenyl group and a2-methylpropenyl group.

When two of R¹″ to R³″ are bonded to each other to form a ring with thesulfur atom, it is preferable that the two of R¹″ to R³″ form a 3 to10-membered ring including the sulfur atom, and it is particularlydesirable that the two of R¹″ to R³″ form a 5 to 7-membered ringincluding the sulfur atom.

When two of R¹″ to R³″ are bonded to each other to form a ring with thesulfur atom, the remaining one of R¹″ to R³″ is preferably an arylgroup. As examples of the aryl group, the same as the above-mentionedaryl groups for R¹″ to R³″ can be given.

Specific examples of the cation moiety of a compound represented by theaforementioned formula (b-1) include triphenylsulfonium,(3,5-dimethylphenyl)diphenyl sulfonium,(4-(2-adamantoxymethyloxy)-3,5-dimethylphenyl)diphenylsulfonium,(4-(2-adamantoxymethyloxy)phenyl)diphenylsulfonium,(4-(tert-butoxycarbonylmethyloxy)phenyl)diphenylsulfonium,(4-(tert-butoxycarbonylmethyloxy)-3,5-dimethylphenyl)diphenylsulfonium,(4-(2-methyl-2-adamantyloxycarbonylmethyloxy)phenyl)diphenylsulfonium,(4-(2-methyl-2-adamantyloxycarbonylmethyloxy)-3,5-dimethylphenyl)diphenylsulfonium, tri(4-methylphenyl)sulfonium,dimethyl(4-hydroxynaphthyl)sulfonium, monophenyldimethylsulfonium,diphenylmonomethylsulfonium, (4-methylphenyl)diphenylsulfonium,(4-methoxyphenyl)diphenylsulfonium, tri(4-tert-butyl)phenylsulfonium,diphenyl(1-(4-methoxy)naphthyl)sulfonium, di(1-naphthyl)phenylsulfonium,1-phenyltetrahydrothiophenium, 1-(4-methylphenyl)tetrahydrothiophenium,1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiophenium,1-(4-methoxynaphthalene-1-yl)tetrahydrothiophenium,1-(4-ethoxynaphthalene-1-yl)tetrahydrothiophenium,1-(4-n-butoxynaphthalene-1-yl)tetrahydrothiophenium,1-phenyltetrahydrothiopyranium,1-(4-hydroxyphenyl)tetrahydrothiopyranium,1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiopyranium and1-(4-methylphenyl)tetrahydrothiopyranium.

Further, Preferable examples of the cation moiety of a compoundrepresented by the aforementioned formula (b-1) include specific cationmoietys shown below.

In the formula, g1 represents a recurring number, and is an integer of 1to 5.

In the formula, g2 and g3 represent recurring numbers, wherein g2 is aninteger of 0 to 20, and g3 is an integer of 0 to 20.

In formula (b-1) above, R⁴″ represents an alkyl group, a halogenatedalkyl group, an aryl group or an alkenyl group which may have asubstituent.

The alkyl group for R⁴″ may be any of linear, branched or cyclic.

The linear or branched alkyl group preferably has 1 to 10 carbon atoms,more preferably 1 to 8 carbon atoms, and most preferably 1 to 4 carbonatoms.

The cyclic alkyl group preferably has 4 to 15 carbon atoms, morepreferably 4 to 10 carbon atoms, and most preferably 6 to 10 carbonatoms.

As an example of the halogenated alkyl group for R⁴″, a group in whichpart of or all of the hydrogen atoms of the aforementioned linear,branched or cyclic alkyl group have been substituted with halogen atomscan be given. Examples of the aforementioned halogen atom include afluorine atom, a chlorine atom, a bromine atom and an iodine atom, and afluorine atom is preferable.

In the halogenated alkyl group, the percentage of the number of halogenatoms based on the total number of halogen atoms and hydrogen atoms(halogenation ratio (%)) is preferably 10 to 100%, more preferably 50 to100%, and most preferably 100%. A higher halogenation ratio ispreferable because the acid strength increases.

The aryl group for R⁴″ is preferably an aryl group of 6 to 20 carbonatoms.

The alkenyl group for R⁴″ is preferably an alkenyl group of 2 to 10carbon atoms.

With respect to R⁴″, the expression “may have a substituent” means thatpart of or all of the hydrogen atoms within the aforementioned alkylgroup, halogenated alkyl group, aryl group or alkenyl group may besubstituted with substituents (atoms other than hydrogen atoms, orgroups).

R⁴″ may have one substituent, or two or more substituents.

Examples of the substituent include a halogen atom, a heteroatom, analkyl group, and a group represented by the formula R^(X)-Q¹- (in theformula, Q¹ represents a divalent linking group containing an oxygenatom; and R^(X) represents a hydrocarbon group of 3 to 30 carbon atomswhich may have a substituent).

Examples of halogen atoms and alkyl groups as substituents for R⁴″include the same halogen atoms and alkyl groups as those described abovewith respect to the halogenated alkyl group for R⁴″.

Examples of heteroatoms include an oxygen atom, a nitrogen atom, and asulfur atom.

In the group represented by formula R^(X)-Q¹-, Q¹ represents a divalentlinking group containing an oxygen atom.

Q¹ may contain an atom other than oxygen. Examples of atoms other thanoxygen include a carbon atom, a hydrogen atom, a sulfur atom and anitrogen atom.

Examples of divalent linking groups containing an oxygen atom includenon-hydrocarbon, oxygen atom-containing linking groups such as an oxygenatom (an ether bond; —O—), an ester bond (—C(═O)—O—), an amido bond(—C(═O)—NH—), a carbonyl group (—C(═O)—) and a carbonate bond(—O—C(═O)—O—); and combinations of the aforementioned non-hydrocarbon,heteroatom-containing linking groups with an alkylene group.

Specific examples of the combinations of the aforementionednon-hydrocarbon, heteroatom-containing linking groups and an alkylenegroup include —R⁹¹—O—, —R⁹²—O—C(═O)—, —C(═O)—O—R⁹³—O—C(═O)— (in theformulas, each of R⁹¹ to R⁹³ independently represents an alkylenegroup).

The alkylene group for R⁹¹ to R⁹³ is preferably a linear or branchedalkylene group, and preferably has 1 to 12 carbon atoms, more preferably1 to 5, and most preferably 1 to 3.

Specific examples of alkylene groups include a methylene group [—CH₂—];alkylmethylene groups such as —CH(CH₃)—, —CH(CH₂CH₃)—, —C(CH₃)₂—,—C(CH₃)(CH₂CH₃)—, —C(CH₃)(CH₂CH₂CH₃)— and —C(CH₂CH₃)₂—; an ethylenegroup [—CH₂CH₂—]; alkylethylene groups such as —CH(CH₃)CH₂—,—CH(CH₃)CH(CH₃)—, —C(CH₃)₂CH₂— and —CH(CH₂CH₃)CH₂—; a trimethylene group(n-propylene group) [—CH₂CH₂CH₂—]; alkyltrimethylene groups such as—CH(CH₃)CH₂CH₂— and —CH₂CH(CH₃)CH₂—; a tetramethylene group[—CH₂CH₂CH₂CH₂—]; alkyltetramethylene groups such as —CH(CH₃)CH₂CH₂CH₂—and —CH₂CH(CH₃)CH₂CH₂—; and a pentamethylene group [—CH₂CH₂CH₂CH₂CH₂—].

Q¹ is preferably a divalent linking group containing an ester linkage orether linkage, and more preferably a group of —R⁹¹—O—, —R⁹²—O—C(═O)— or—C(═O)—O—R⁹³—O—C(═O)—.

In the group represented by the formula R^(X)-Q¹-, the hydrocarbon groupfor R^(X) may be either an aromatic hydrocarbon group or an aliphatichydrocarbon group.

The aromatic hydrocarbon group is a hydrocarbon group having an aromaticring. The aromatic hydrocarbon ring preferably has 3 to 30 carbon atoms,more preferably 5 to 30, still more preferably 5 to 20, still morepreferably 6 to 15, and most preferably 6 to 12. Here, the number ofcarbon atoms within a substituent(s) is not included in the number ofcarbon atoms of the aromatic hydrocarbon group.

Specific examples of aromatic hydrocarbon groups include an aryl groupwhich is an aromatic hydrocarbon ring having one hydrogen atom removedtherefrom, such as a phenyl group, a biphenyl group, a fluorenyl group,a naphthyl group, an anthryl group or a phenanthryl group; and analkylaryl group such as a benzyl group, a phenethyl group, a1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethylgroup, or a 2-naphthylethyl group. The alkyl chain within the arylalkylgroup preferably has 1 to 4 carbon atoms, more preferably 1 or 2, andmost preferably 1.

The aromatic hydrocarbon group may have a substituent. For example, partof the carbon atoms constituting the aromatic ring within the aromatichydrocarbon group may be substituted with a heteroatom, or a hydrogenatom bonded to the aromatic ring within the aromatic hydrocarbon groupmay be substituted with a substituent.

In the former example, a heteroaryl group in which part of the carbonatoms constituting the ring within the aforementioned aryl group hasbeen substituted with a heteroatom such as an oxygen atom, a sulfur atomor a nitrogen atom, and a heteroarylalkyl group in which part of thecarbon atoms constituting the aromatic hydrocarbon ring within theaforementioned arylalkyl group has been substituted with theaforementioned heteroatom can be used.

In the latter example, as the substituent for the aromatic hydrocarbongroup, an alkyl group, an alkoxy group, a halogen atom, a halogenatedalkyl group, a hydroxyl group, an oxygen atom (═O) or the like can beused.

The alkyl group as the substituent for the aromatic hydrocarbon group ispreferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, anethyl group, a propyl group, an n-butyl group or a tert-butyl group isparticularly desirable.

The alkoxy group as the substituent for the aromatic hydrocarbon groupis preferably an alkoxy group having 1 to 5 carbon atoms, morepreferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxygroup, n-butoxy group or tert-butoxy group, and most preferably amethoxy group or an ethoxy group.

Examples of the halogen atom as the substituent for the aromatichydrocarbon group include a fluorine atom, a chlorine atom, a bromineatom and an iodine atom, and a fluorine atom is preferable.

An example of the halogenated alkyl group as the substituent for thearomatic hydrocarbon group includes a group in which part or all of thehydrogen atoms within the aforementioned alkyl group have beensubstituted with the aforementioned halogen atoms.

The aliphatic hydrocarbon group for R^(X) may be either a saturatedaliphatic hydrocarbon group, or an unsaturated aliphatic hydrocarbongroup. Further, the aliphatic hydrocarbon group may be linear, branchedor cyclic.

In the aliphatic hydrocarbon group for R^(X), part of the carbon atomsconstituting the aliphatic hydrocarbon group may be substituted with asubstituent group containing a heteroatom, or part or all of thehydrogen atoms constituting the aliphatic hydrocarbon group may besubstituted with a substituent group containing a heteroatom.

As the “heteroatom” for R^(X), there is no particular limitation as longas it is an atom other than carbon and hydrogen. Examples of heteroatomsinclude a halogen atom, an oxygen atom, a sulfur atom and a nitrogenatom.

Examples of the halogen atom include a fluorine atom, a chlorine atom,an iodine atom and a bromine atom.

The substituent group containing a heteroatom may consist of aheteroatom, or may be a group containing a group or atom other than aheteroatom.

Specific examples of the substituent group for substituting part of thecarbon atoms include —O—, —C(═O)—O—, —C(═O)—, —O—C(═O)—O—, —C(═O)—NH—,—NH— (the H may be replaced with a substituent such as an alkyl group oran acyl group), —S—, —S(═O)₂— and —S(═O)₂—O—. When the aliphatichydrocarbon group is cyclic, the aliphatic hydrocarbon group may containany of these substituent groups in the ring structure.

Examples of the substituent group for substituting part or all of thehydrogen atoms include an alkoxy group, a halogen atom, a halogenatedalkyl group, a hydroxyl group, an oxygen atom (═O) and a cyano group.

The aforementioned alkoxy group is preferably an alkoxy group having 1to 5 carbon atoms, more preferably a methoxy group, ethoxy group,n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group,and most preferably a methoxy group or an ethoxy group.

Examples of the aforementioned halogen atom include a fluorine atom, achlorine atom, a bromine atom and an iodine atom, and a fluorine atom ispreferable.

An example of the aforementioned halogenated alkyl group includes agroup in which part or all of the hydrogen atoms within an alkyl groupof 1 to 5 carbon atoms (e.g., a methyl group, an ethyl group, a propylgroup, an n-butyl group or a tert-butyl group) have been substitutedwith the aforementioned halogen atoms.

As the aliphatic hydrocarbon group, a linear or branched saturatedhydrocarbon group, a linear or branched monovalent unsaturatedhydrocarbon group, or a cyclic aliphatic hydrocarbon group (aliphaticcyclic group) is preferable.

The linear saturated hydrocarbon group (alkyl group) preferably has 1 to20 carbon atoms, more preferably 1 to 15, and most preferably 1 to 10.Specific examples include a methyl group, an ethyl group, a propylgroup, a butyl group, a pentyl group, a hexyl group, a heptyl group, anoctyl group, a nonyl group, a decanyl group, an undecyl group, a dodecylgroup, a tridecyl group, an isotridecyl group, a tetradecyl group, apentadecyl group, a hexadecyl group, an isohexadecyl group, a heptadecylgroup, an octadecyl group, a nonadecyl group, an icosyl group, ahenicosyl group and a docosyl group.

The branched saturated hydrocarbon group (alkyl group) preferably has 3to 20 carbon atoms, more preferably 3 to 15, and most preferably 3 to10. Specific examples include a 1-methylethyl group, a 1-methylpropylgroup, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutylgroup, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutylgroup, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentylgroup and a 4-methylpentyl group.

The unsaturated hydrocarbon group preferably has 2 to 10 carbon atoms,more preferably 2 to 5, still more preferably 2 to 4, and mostpreferably 3. Examples of linear monovalent unsaturated hydrocarbongroups include a vinyl group, a propenyl group (an allyl group) and abutynyl group. Examples of branched monovalent unsaturated hydrocarbongroups include a 1-methylpropenyl group and a 2-methylpropenyl group.

Among the above-mentioned examples, as the unsaturated hydrocarbongroup, a propenyl group is particularly desirable.

The aliphatic cyclic group may be either a monocyclic group or apolycyclic group. The aliphatic cyclic group preferably has 3 to 30carbon atoms, more preferably 5 to 30, still more preferably 5 to 20,still more preferably 6 to 15, and most preferably 6 to 12.

As the aliphatic cyclic group, a group in which one or more hydrogenatoms have been removed from a monocycloalkane or a polycycloalkane suchas a bicycloalkane, tricycloalkane or tetracycloalkane can be used.Specific examples include groups in which one or more hydrogen atomshave been removed from a monocycloalkane such as cyclopentane orcyclohexane; and groups in which one or more hydrogen atoms have beenremoved from a polycycloalkane such as adamantane, norbornane,isobornane, tricyclodecane or tetracyclododecane.

When the aliphatic cyclic group does not contain a heteroatom-containingsubstituent group in the ring structure thereof, the aliphatic cyclicgroup is preferably a polycyclic group, more preferably a group in whichone or more hydrogen atoms have been removed from a polycycloalkane, anda group in which one or more hydrogen atoms have been removed fromadamantane is particularly desirable.

When the aliphatic cyclic group contains a heteroatom-containingsubstituent group in the ring structure thereof, theheteroatom-containing substituent group is preferably —O—, —C(═O)—O—,—S—, —S(═O)₂— or —S(═O)₂—O—. Specific examples of such aliphatic cyclicgroups include groups represented by formulas (L1) to (L6) and (S1) to(S4) shown below.

In the formula, Q″ represents an alkylene group of 1 to 5 carbon atoms,—O—, —S—, —O—R⁹⁴— or —S—R⁹⁵— (wherein each of R⁹⁴ and R⁹⁵ independentlyrepresents an alkylene group of 1 to 5 carbon atoms); and m represents 0or 1.

As the alkylene group for Q″, R⁹⁴ and R⁹⁵, the same alkylene groups asthose described above for R⁹¹ to R⁹³ can be used.

In these aliphatic cyclic groups, part of the hydrogen atoms bonded tothe carbon atoms constituting the ring structure may be substituted witha substituent. Examples of substituents include an alkyl group, analkoxy group, a halogen atom, a halogenated alkyl group, a hydroxylgroup and an oxygen atom (═O).

As the alkyl group, an alkyl group of 1 to 5 carbon atoms is preferable,and a methyl group, an ethyl group, a propyl group, an n-butyl group ora tert-butyl group is particularly desirable.

As the alkoxy group and the halogen atom, the same groups as thesubstituent groups for substituting part or all of the hydrogen atomscan be used.

Among the above-mentioned examples, as such R^(X), a cyclic group whichmay have a substituent is preferable. The cyclic group may be either anaromatic hydrocarbon group which may have a substituent, or an aliphaticcyclic group which may have a substituent, and an aliphatic cyclic groupwhich may have a substituent is preferable.

As the aromatic hydrocarbon group, a naphthyl group which may have asubstituent, or a phenyl group which may have a substituent ispreferable.

As the aliphatic cyclic group which may have a substituent, an aliphaticpolycyclic group which may have a substituent is preferable. As thealiphatic polycyclic group, the aforementioned group in which one ormore hydrogen atoms have been removed from a polycycloalkane, and groupsrepresented by the aforementioned formulas (L2) to (L5), (S3) and (S4)are preferable.

Further, it is particularly desirable that R^(X) have a polar moiety,because it results in improved lithographic properties and resistpattern shape.

Specific examples of R^(X) having a polar moiety include those in whicha part of the carbon atoms constituting the aliphatic hydrocarbon groupfor X is substituted with a substituent group containing a heteroatomsuch as —O—, —C(═O)—O—, —C(═O)—, —O—C(═O)—O—, —C(═O)—NH—, —NH— (whereinH may be substituted with a substituent such as an alkyl group or anacyl group), —S—, —S(═O)₂— and —S(═O)₂—O—.

Among the above-mentioned examples, R⁴″ preferably has R^(X)-Q¹- as asubstituent. In such a case, R⁴″ is preferably a group represented bythe formula R^(X)-Q¹-Y¹— (in the formula, Q¹ and R^(X) are the same asdefined above; and Y¹ represents an alkylene group of 1 to 4 carbonatoms which may have a substituent, or a fluorinated alkylene group of 1to 4 carbon atoms which may have a substituent).

In the group represented by the formula R^(X)-Q¹-Y¹—, as the alkylenegroup for Y¹, the same alkylene group as those described above for Q¹ inwhich the number of carbon atoms is 1 to 4 can be used.

As the fluorinated alkylene group for Y¹, the aforementioned alkylenegroup in which part or all of the hydrogen atoms have been substitutedwith fluorine atoms can be used.

Specific examples of Y¹ include —CF₂CF₂—, —CF₂CF₂CF₂—, —CF(CF₃)CF₂—,—CF(CF₂CF₃)—, —C(CF₃)₂—, —CF₂CF₂CF₂CF₂—, —CF(CF₃)CF₂CF₂—,—CF₂CF(CF₃)CF₂—, —CF(CF₃)CF(CF₃)—, —C(CF₃)₂CF₂—, —CF(CF₂CF₃)CF₂—,—CF(CF₂CF₂CF₃)—, —C(CF₃)(CF₂CF₃)—; —CHF—, —CH₂CF₂—, —CH₂CH₂CF₂—,—CH₂CF₂CF₂—, —CH(CF₃)CH₂—, —CH(CF₂CF₃)—, —C(CH₃)(CF₃)—, —CH₂CH₂CH₂CF₂—,—CH₂CH₂CF₂CF₂—, —CH(CF₃)CH₂CH₂—, —CH₂CH(CF₃)CH₂—, —CH(CF₃)CH(CF₃)—,—C(CF₃)₂CH₂—; —CH₂CH₂—, —CH₂CH₂CH₂—, —CH(CH₃)CH₂—, —CH(CH₂CH₃)—,—C(CH₃)₂—, —CH₂CH₂CH₂CH₂—, —CH(CH₃)CH₂CH₂—, —CH₂CH(CH₃)CH₂—,—CH(CH₃)CH(CH₃)—, —C(CH₃)₂CH₂—, —CH(CH₂CH₃)CH₂—, —CH(CH₂CH₂CH₃)—, and—C(CH₃)(CH₂CH₃)—.

Y¹ is preferably a fluorinated alkylene group, and particularlypreferably a fluorinated alkylene group in which the carbon atom bondedto the adjacent sulfur atom is fluorinated. Examples of such fluorinatedalkylene groups include —CF₂CF₂—, —CF₂CF₂CF₂—, —CF(CF₃)CF₂—,—CF₂CF₂CF₂CF₂—, —CF(CF₃)CF₂CF₂—, —CF₂CF(CF₃)CF₂—, —CF(CF₃)CF(CF₃)—,—C(CF₃)₂CF₂—, —CF(CF₂CF₃)CF₂—; —CH₂CF₂—, —CH₂CH₂CF₂—, —CH₂CF₂CF₂—;—CH₂CH₂CH₂CF₂—, —CH₂CH₂CF₂CF₂—, and —CH₂CF₂CF₂CF₂—.

Of these, —CF₂CF₂—, —CF₂CF₂CF₂— or CH₂CF₂CF₂— is preferable, —CF₂CF₂— or—CF₂CF₂CF₂— is more preferable, and —CF₂— is particularly desirable.

The alkylene group or fluorinated alkylene group may have a substituent.The alkylene group or fluorinated alkylene group “has a substituent”means that part or all of the hydrogen atoms or fluorine atoms in thealkylene group or fluorinated alkylene group have been substituted withgroups other than hydrogen atoms and fluorine atoms.

Examples of substituents which the alkylene group or fluorinatedalkylene group may have include an alkyl group of 1 to 4 carbon atoms,an alkoxy group of 1 to 4 carbon atoms, and a hydroxyl group.

In formula (b-2), each of R⁵″ and R⁶″ independently represents an arylgroup, alkyl group or alkenyl group which may have a substituent.

Further, since lithography properties and the shape of the resistpattern are improved, among R⁵″ and R⁶″, at least one is preferably arylgroup. It is more preferable that both R⁵″ and R⁶″ represent an arylgroup.

As the aryl group for R⁵″ and R⁶″, the same as the aryl groups for R¹″to R³″ can be used.

As the alkyl group for R⁵″ and R⁶″, the same as the alkyl groups for R¹″to R³″ can be used.

As the alkenyl group for R⁵″ and R⁶″, the same as the alkenyl groups forR¹″ to R³″ can be used.

It is particularly desirable that both of R⁵″ and R⁶″ represent a phenylgroup.

Specific examples of the cation moiety of a compound represented bygeneral formula (b-2) include diphenyliodonium andbis(4-tert-butylphenyl)iodonium.

As R⁴″ in formula (b-2), the same groups as those mentioned above forR⁴″ in formula (b-1) can be used.

Specific examples of suitable onium salt acid generators represented byformula (b-1) or (b-2) include diphenyliodoniumtrifluoromethanesulfonate or nonafluorobutanesulfonate;bis(4-tert-butylphenyl)iodonium trifluoromethanesulfonate ornonafluorobutanesulfonate; triphenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;tri(4-methylphenyl)sulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;dimethyl(4-hydroxynaphthyl)sulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;monophenyldimethylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;diphenylmonomethylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;(4-methylphenyl)diphenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;(4-methoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;tri(4-tert-butyl)phenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate; diphenyl(1-(4-methoxy)naphthyl)sulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;di(1-naphthyl)phenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;1-phenyltetrahydrothiophenium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;1-(4-methylphenyl)tetrahydrothiophenium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiopheniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate;1-(4-methoxynaphthalene-1-yl)tetrahydrothiopheniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate;1-(4-ethoxynaphthalene-1-yl)tetrahydrothiopheniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate;1-(4-n-butoxynaphthalene-1-yl)tetrahydrothiopheniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate; 1-phenyltetrahydrothiopyraniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate; 1-(4-hydroxyphenyl)tetrahydrothiopyraniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate;1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiopyraniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate; and 1-(4-methylphenyl)tetrahydrothiopyraniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate.

It is also possible to use each of onium salts in which the anion moietyof these onium salts is replaced by an alkyl sulfonate, such asmethanesulfonate, n-propanesulfonate, n-butanesulfonate,n-octanesulfonate, 1-adamantanesulfonate or 2-norbornanesulfonate; orreplaced by a sulfonate, such as d-camphor-10-sulfonate,benzenesulfonate, perfluorobenzenesulfonate or p-toluenesulfonate.

Furthermore, onium salts in which the anion moiety of these onium saltsare replaced by an anion represented by any one of formulas (b1) to (b8)shown below can be used.

In the formulas, y represents an integer of 1 to 3; each of q1 and q2independently represents an integer of 1 to 5; q3 represents an integerof 1 to 12; t3 represents an integer of 1 to 3; each of r1 and r2independently represents an integer of 0 to 3; i represents an integerof 1 to 20; R⁵⁰ represents a substituent; each of m1 to m5 independentlyrepresents 0 or 1; each of v0 to v5 independently represents an integerof 0 to 3; each of w1 to w5 independently represents an integer of 0 to3; and Q″ is the same as defined above.

As the substituent for R⁵⁰, the same groups as those which theaforementioned aliphatic hydrocarbon group or aromatic hydrocarbon groupfor R^(X) may have as a substituent can be used.

If there are two or more of the R⁵⁰ group, as indicated by the valuesr1, r2, and w1 to w5, then the two or more of the R⁵⁰ groups may be thesame or different from each other.

Further, onium salt-based acid generators in which the anion moiety(R⁴″SO₃ ⁻) in general formula (b-1) or (b-2) is replaced by an anionmoiety represented by general formula (b-3) or (b-4) shown below (thecation moiety is the same cation moiety as the aforementioned formula(b-1) or (b-2)) may be used.

In the formulas, X″ represents an alkylene group of 2 to 6 carbon atomsin which at least one hydrogen atom has been substituted with a fluorineatom; and each of Y″ and Z″ independently represents an alkyl group of 1to 10 carbon atoms in which at least one hydrogen atom has beensubstituted with a fluorine atom.

X″ represents a linear or branched alkylene group in which at least onehydrogen atom has been substituted with a fluorine atom, and thealkylene group has 2 to 6 carbon atoms, preferably 3 to 5 carbon atoms,and most preferably 3 carbon atoms.

Each of Y″ and Z″ independently represents a linear or branched alkylgroup in which at least one hydrogen atom has been substituted with afluorine atom, and the alkyl group has 1 to 10 carbon atoms, preferably1 to 7 carbon atoms, and most preferably 1 to 3 carbon atoms.

The smaller the number of carbon atoms of the alkylene group for X″ orthose of the alkyl group for Y″ and Z″ within the above-mentioned rangeof the number of carbon atoms, the more the solubility in a resistsolvent is improved.

Further, in the alkylene group for X″ or the alkyl group for Y″ and Z″,it is preferable that the number of hydrogen atoms substituted withfluorine atoms be as large as possible because the acid strengthincreases and the transparency to high energy radiation of 200 nm orless or electron beam is improved.

The fluorination ratio of the alkylene group or alkyl group ispreferably from 70 to 100%, more preferably from 90 to 100%, and it isparticularly desirable that the alkylene group or alkyl group be aperfluoroalkylene group or perfluoroalkyl group in which all hydrogenatoms are substituted with fluorine atoms.

Further, an onium salt-based acid generator in which the anion moiety(R⁴″SO₃ ⁻) in general formula (b-1) or (b-2) has been replaced withR^(h)—COO⁻ (in the formula, R^(h) represents an alkyl group or afluorinated alkyl group) can also be used as the onium salt-based acidgenerator (the cation moiety is the same as that in general formula(b-1) or (b-2)).

In the formula above, as R^(h), the same groups as those described abovefor R⁴″ can be used.

Specific examples of the group represented by the formula “R^(h)—COO⁻”include a trifluoroacetic acid ion, an acetic acid ion, and a1-adamantanecarboxylic acid ion.

Furthermore, as an onium salt-based acid generator, a sulfonium salthaving a cation represented by general formula (b-5) or (b-6) shownbelow in a cation moiety may be used.

In formulas (b-5) and (b-6) above, each of R⁸¹ to R⁸⁶ independentlyrepresents an alkyl group, an acetyl group, an alkoxy group, a carboxygroup, a hydroxyl group or a hydroxyalkyl group; each of n₁ to n₅independently represents an integer of 0 to 3; and n₆ represents aninteger of 0 to 2.

With respect to R⁸¹ to R⁸⁶, the alkyl group is preferably an alkyl groupof 1 to 5 carbon atoms, more preferably a linear or branched alkylgroup, and most preferably a methyl group, ethyl group, propyl group,isopropyl group, n-butyl group or tert-butyl group.

The alkoxy group is preferably an alkoxy group of 1 to 5 carbon atoms,more preferably a linear or branched alkoxy group, and most preferably amethoxy group or ethoxy group.

The hydroxyalkyl group is preferably the aforementioned alkyl group inwhich one or more hydrogen atoms have been substituted with hydroxygroups, and examples thereof include a hydroxymethyl group, ahydroxyethyl group and a hydroxypropyl group.

If there are two or more of an individual R⁸¹ to R⁸⁶ group, as indicatedby the corresponding value of n₁ to n₆, then the two or more of theindividual R⁸¹ to R⁸⁶ group may be the same or different from eachother.

n₁ is preferably 0 to 2, more preferably 0 or 1, and still morepreferably 0.

It is preferable that n₂ and n₃ each independently represents 0 or 1,and more preferably 0.

n₄ is preferably 0 to 2, and more preferably 0 or 1.

n₅ is preferably 0 or 1, and more preferably 0.

n₆ is preferably 0 or 1, and more preferably 1.

Preferable examples of the cation represented by formula (b-5) or (b-6)include the following.

Further, the sulfonium salt having a cation represented by generalformula (b-7) or (b-8) shown below in a cation moiety can also be used.

In formulas (b-7) and (b-8), each of R⁹ and R¹⁰ independently representsa phenyl group or naphthyl group which may have a substituent, an alkylgroup of 1 to 5 carbon atoms, an alkoxy group or a hydroxy group.Examples of the substituent are the same as the substituents describedabove in relation to the substituted aryl group for R¹″ to R³″ (i.e., analkyl group, an alkoxy group, an alkoxyalkyloxy group, analkoxycarbonylalkyloxy group, a halogen atom, a hydroxy group, an oxogroup (═O), an aryl group, —C(═O)—O—R⁶′, —O—C(═O)—R⁷′, —O—R⁸′, a groupin which R⁵⁶′ in the aforementioned general formula —O—R⁵⁰—C(═O)—O—R⁵⁶has been substituted with R⁵⁶′).

R⁴′ represents an alkylene group of 1 to 5 carbon atoms.

u is an integer of 1 to 3, and most preferably 1 or 2.

Preferable examples of the cation represented by formula (b-7) or (b-8)are shown below. In the formulas, R^(C) represents the same substituentsdescribed above in relation to the aforementioned substituted aryl group(i.e., an alkyl group, an alkoxy group, an alkoxyalkyloxy group, analkoxycarbonylalkyloxy group, a halogen atom, a hydroxy group, an oxogroup (═O), an aryl group, —C(═O)—O—R⁶′, —O—C(═O)—R⁷′,

The anion moiety of the sulfonium salt having a cation represented bygeneral formula (b-5) to (b-8) in a cation moiety is not particularlylimited, and the same anion moieties for onium salt-based acidgenerators which have been proposed may be used. Examples of such anionmoieties include fluorinated alkylsulfonic acid ions such as anionmoieties (R⁴″SO₃ ⁻) for onium salt-based acid generators represented bygeneral formula (b-1) or (b-2) shown above; and anions represented bygeneral formula (b-3) or (b-4) shown above, or an anion represented byany one of the aforementioned formulas (b1) to (b8).

In the present description, an oximesulfonate-based acid generator is acompound having at least one group represented by general formula (B-1)shown below, and has a feature of generating acid by irradiation(exposure). Such oximesulfonate acid generators are widely used for achemically amplified resist composition, and can be appropriatelyselected.

In formula (B-1), each of R³¹ and R³² independently represents anorganic group.

The organic group for R³¹ and R³² refers to a group containing a carbonatom, and may include atoms other than carbon atoms (e.g., a hydrogenatom, an oxygen atom, a nitrogen atom, a sulfur atom, a halogen atom(such as a fluorine atom and a chlorine atom) and the like).

As the organic group for R³¹, a linear, branched, or cyclic alkyl groupor aryl group is preferable. The alkyl group or the aryl group may havea substituent. The substituent is not particularly limited, and examplesthereof include a fluorine atom and a linear, branched, or cyclic alkylgroup having 1 to 6 carbon atoms. The alkyl group or the aryl group “hasa substituent” means that part or all of the hydrogen atoms of the alkylgroup or the aryl group are substituted with a substituent.

The alkyl group preferably has 1 to 20 carbon atoms, more preferably 1to 10 carbon atoms, still more preferably 1 to 8 carbon atoms, stillmore preferably 1 to 6 carbon atoms, and most preferably 1 to 4 carbonatoms. As the alkyl group, a partially or completely halogenated alkylgroup (hereinafter, sometimes referred to as a “halogenated alkylgroup”) is particularly desirable. The “partially halogenated alkylgroup” refers to an alkyl group in which part of the hydrogen atoms aresubstituted with halogen atoms and the “completely halogenated alkylgroup” refers to an alkyl group in which all of the hydrogen atoms aresubstituted with halogen atoms. Examples of halogen atoms includefluorine atoms, chlorine atoms, bromine atoms and iodine atoms, andfluorine atoms are particularly desirable. In other words, thehalogenated alkyl group is preferably a fluorinated alkyl group.

The aryl group preferably has 4 to 20 carbon atoms, more preferably 4 to10 carbon atoms, and most preferably 6 to 10 carbon atoms. As the arylgroup, partially or completely halogenated aryl group is particularlydesirable. The “partially halogenated aryl group” refers to an arylgroup in which some of the hydrogen atoms are substituted with halogenatoms and the “completely halogenated aryl group” refers to an arylgroup in which all of hydrogen atoms are substituted with halogen atoms.

As R³¹, an alkyl group of 1 to 4 carbon atoms which has no substituentor a fluorinated alkyl group of 1 to 4 carbon atoms is particularlydesirable.

As the organic group for R³², a linear, branched, or cyclic alkyl group,aryl group, or cyano group is preferable. Examples of the alkyl groupand the aryl group for R³² include the same alkyl groups and aryl groupsas those described above for R³¹.

As R³², a cyano group, an alkyl group of 1 to 8 carbon atoms having nosubstituent or a fluorinated alkyl group of 1 to 8 carbon atoms isparticularly desirable.

Preferred examples of the oxime sulfonate acid generator includecompounds represented by general formula (B-2) or (B-3) shown below.

In the formula, R³³ represents a cyano group, an alkyl group having nosubstituent or a halogenated alkyl group; R³⁴ represents an aryl group;and R³⁵ represents an alkyl group having no substituent or a halogenatedalkyl group.

In the formula, R³⁶ represents a cyano group, an alkyl group having nosubstituent or a halogenated alkyl group; R³⁷ represents a divalent ortrivalent aromatic hydrocarbon group; R³⁸ represents an alkyl grouphaving no substituent or a halogenated alkyl group; and p″ represents 2or 3.

In general formula (B-2), the alkyl group having no substituent or thehalogenated alkyl group for R³³ preferably has 1 to 10 carbon atoms,more preferably 1 to 8 carbon atoms, and most preferably 1 to 6 carbonatoms.

As R³³, a halogenated alkyl group is preferable, and a fluorinated alkylgroup is more preferable.

The fluorinated alkyl group for R³³ preferably has 50% or more of thehydrogen atoms thereof fluorinated, more preferably 70% or more, andmost preferably 90% or more.

Examples of the aryl group for R³⁴ include groups in which one hydrogenatom has been removed from an aromatic hydrocarbon ring, such as aphenyl group, a biphenyl group, a fluorenyl group, a naphthyl group, ananthryl group, and a phenanthryl group, and heteroaryl groups in whichsome of the carbon atoms constituting the ring(s) of these groups aresubstituted with heteroatoms such as an oxygen atom, a sulfur atom, anda nitrogen atom. Of these, a fluorenyl group is preferable.

The aryl group for R³⁴ may have a substituent such as an alkyl group of1 to 10 carbon atoms, a halogenated alkyl group, or an alkoxy group. Thealkyl group and halogenated alkyl group as the substituent preferablyhas 1 to 8 carbon atoms, and more preferably 1 to 4 carbon atoms.Further, the halogenated alkyl group is preferably a fluorinated alkylgroup.

The alkyl group having no substituent or the halogenated alkyl group forR³⁵ preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbonatoms, and most preferably 1 to 6 carbon atoms.

As R³⁵, a halogenated alkyl group is preferable, and a fluorinated alkylgroup is more preferable.

In terms of enhancing the strength of the acid generated, thefluorinated alkyl group for R³⁵ preferably has 50% or more of thehydrogen atoms fluorinated, more preferably 70% or more, still morepreferably 90% or more. A completely fluorinated alkyl group in which100% of the hydrogen atoms are substituted with fluorine atoms isparticularly desirable.

In general formula (B-3), as the alkyl group having no substituent andthe halogenated alkyl group for R³⁶, the same alkyl group having nosubstituent and the halogenated alkyl group described above for R³³ canbe used.

Examples of the divalent or trivalent aromatic hydrocarbon group for R³⁷include groups in which one or two hydrogen atoms have been removed fromthe aryl group for R³⁴.

As the alkyl group having no substituent or the halogenated alkyl groupfor R³⁸, the same one as the alkyl group having no substituent or thehalogenated alkyl group for R³⁵ can be used.

p″ is preferably 2.

Specific examples of suitable oxime sulfonate acid generators includeα-(p-toluenesulfonyloxyimino)-benzyl cyanide,α-(p-chlorobenzenesulfonyloxyimino)-benzyl cyanide,α-(4-nitrobenzenesulfonyloxyimino)-benzyl cyanide,α-(4-nitro-2-trifluoromethylbenzenesulfonyloxyimino)-benzyl cyanide,α-(benzenesulfonyloxyimino)-4-chlorobenzyl cyanide,α-(benzenesulfonyloxyimino)-2,4-dichlorobenzyl cyanide,α-(benzenesulfonyloxyimino)-2,6-dichlorobenzyl cyanide,α-(benzenesulfonyloxyimino)-4-methoxybenzyl cyanide,α-(2-chlorobenzenesulfonyloxyimino)-4-methoxybenzyl cyanide,α-(benzenesulfonyloxyimino)-thien-2-yl acetonitrile,α-(4-dodecylbenzenesulfonyloxyimino)benzyl cyanide,α-[(p-toluenesulfonyloxyimino)-4-methoxyphenyl]acetonitrile,α-[(dodecylbenzenesulfonyloxyimino)-4-methoxyphenyl]acetonitrile,α-(tosyloxyimino)-4-thienyl cyanide,α-(methylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,α-(methylsulfonyloxyimino)-1-cyclohexenyl acetonitrile,α-(methylsulfonyloxyimino)-1-cycloheptenyl acetonitrile,α-(methylsulfonyloxyimino)-1-cyclooctenyl acetonitrile,α-(trifluoromethylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,α-(trifluoromethylsulfonyloxyimino)-cyclohexyl acetonitrile,α-(ethylsulfonyloxyimino)-ethyl acetonitrile,α-(propylsulfonyloxyimino)-propyl acetonitrile,α-(cyclohexylsulfonyloxyimino)-cyclopentyl acetonitrile,α-(cyclohexylsulfonyloxyimino)-cyclohexyl acetonitrile,α-(cyclohexylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,α-(ethylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,α-(isopropylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,α-(n-butylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,α-(ethylsulfonyloxyimino)-1-cyclohexenyl acetonitrile,α-(isopropylsulfonyloxyimino)-1-cyclohexenyl acetonitrile,α-(n-butylsulfonyloxyimino)-1-cyclohexenyl acetonitrile,α-(methylsulfonyloxyimino)-phenyl acetonitrile,α-(methylsulfonyloxyimino)-p-methoxyphenyl acetonitrile,α-(trifluoromethylsulfonyloxyimino)-phenyl acetonitrile,α-(trifluoromethylsulfonyloxyimino)-p-methoxyphenyl acetonitrile,α-(ethylsulfonyloxyimino)-p-methoxyphenyl acetonitrile,α-(propylsulfonyloxyimino)-p-methylphenyl acetonitrile, andα-(methylsulfonyloxyimino)-p-bromophenyl acetonitrile.

Further, oxime sulfonate acid generators disclosed in JapaneseUnexamined Patent Application, First Publication No. Hei 9-208554(Chemical Formulas 18 and 19 shown in paragraphs [0012] to [0014]) andoxime sulfonate acid generators disclosed in WO 2004/074242A2 (Examples1 to 40 described at pages 65 to 85) may be preferably used.

Furthermore, as preferable examples, the following can be used.

Of the aforementioned diazomethane acid generators, specific examples ofsuitable bisalkyl or bisaryl sulfonyl diazomethanes includebis(isopropylsulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane,bis(1,1-dimethylethylsulfonyl)diazomethane,bis(cyclohexylsulfonyl)diazomethane, andbis(2,4-dimethylphenylsulfonyl)diazomethane.

Further, diazomethane acid generators disclosed in Japanese UnexaminedPatent Application, First Publication No. Hei 11-035551, JapaneseUnexamined Patent Application, First Publication No. Hei 11-035552 andJapanese Unexamined Patent Application, First Publication No. Hei11-035573 may be preferably used.

Furthermore, as examples of poly(bis-sulfonyl)diazomethanes, thosedisclosed in Japanese Unexamined Patent Application, First PublicationNo. Hei 11-322707, including1,3-bis(phenylsulfonyldiazomethylsulfonyl)propane,1,4-bis(phenylsulfonyldiazomethylsulfonyl)butane,1,6-bis(phenylsulfonyldiazomethylsulfonyl)hexane,1,10-bis(phenylsulfonyldiazomethylsulfonyl)decane,1,2-bis(cyclohexylsulfonyldiazomethylsulfonyl)ethane,1,3-bis(cyclohexylsulfonyldiazomethylsulfonyl)propane,1,6-bis(cyclohexylsulfonyldiazomethylsulfonyl)hexane, and1,10-bis(cyclohexylsulfonyldiazomethylsulfonyl)decane, may be given.

As the component (B), one type of acid generator described above may beused, or two or more types of the acid generators may be used incombination.

In the positive resist composition of the present invention, the amountof the component (B) relative to 100 parts by weight of the component(A) is preferably 0.5 to 60 parts by weight, more preferably 1 to 50parts by weight, and still more preferably 1 to 40 parts by weight. Whenthe amount of the component (B) is within the above-mentioned range,formation of a resist pattern can be satisfactorily performed. Further,when each component of the resist composition is dissolved in theorganic solvent, by virtue of the above-mentioned range, a uniformsolution can be obtained and the storage stability becomes satisfactory.

<Optional Components>

The resist composition of the present invention may include anitrogen-containing organic compound (D) which does not fall under thecategory of the component (A) or (B) (hereafter referred to as thecomponent (D)), as long as the effects of the present invention are notimpaired.

As the component (D), there is no particular limitation as long as itfunctions as an acid diffusion control agent, i.e., a quencher whichtraps the acid generated from the component (B) upon exposure. Amultitude of these components (D) have already been proposed, and any ofthese known compounds may be used. Examples of the component (D) includean aliphatic amine and an aromatic amine, although an aliphatic amine,and particularly a secondary aliphatic amine or tertiary aliphatic amineis preferable.

An aliphatic amine is an amine having one or more aliphatic groups, andthe aliphatic groups preferably have 1 to 20 carbon atoms.

Examples of these aliphatic amines include amines in which at least onehydrogen atom of ammonia (NH₃) has been substituted with an alkyl groupor hydroxyalkyl group of no more than 20 carbon atoms (i.e., alkylaminesor alkylalcoholamines), and cyclic amines.

The alkyl group and the alkyl group for the hydroxyalkyl group may beany of linear, branched or cyclic.

When the alkyl group is linear or branched, the alkyl group preferablyhas 2 to 20 carbon atoms, and more preferably 2 to 8 carbon atoms.

When the alkyl group is cyclic (i.e., a cycloalkyl group), the number ofcarbon atoms is preferably 3 to 30, more preferably 3 to 20, still morepreferably 3 to 15, still more preferably 4 to 12, and most preferably 5to 10. The alkyl group may be monocyclic or polycyclic. Examples thereofinclude groups in which one or more of the hydrogen atoms have beenremoved from a monocycloalkane; and groups in which one or more of thehydrogen atoms have been removed from a polycycloalkane such as abicycloalkane, a tricycloalkane, or a tetracycloalkane. Specificexamples of the monocycloalkane include cyclopentane and cyclohexane.Specific examples of the polycycloalkane include adamantane, norbornane,isobornane, tricyclodecane and tetracyclododecane.

Specific examples of the alkylamines include monoalkylamines such asn-hexylamine, n-heptylamine, n-octylamine, n-nonylamine, andn-decylamine; dialkylamines such as diethylamine, di-n-propylamine,di-n-heptylamine, di-n-octylamine, and dicyclohexylamine; andtrialkylamines such as trimethylamine, triethylamine, tri-n-propylamine,tri-n-butylamine, tri-n-hexylamine, tri-n-pentylamine,tri-n-heptylamine, tri-n-octylamine, tri-n-nonylamine, tri-n-decylamine,and tri-n-dodecylamine.

Specific examples of the alkylalcoholamines include diethanolamine,triethanolamine, diisopropanolamine, triisopropanolamine,di-n-octanolamine, tri-n-octanolamine, stearyldiethanolamine andlaurildiethanolamine.

Examples of the cyclic amine include heterocyclic compounds containing anitrogen atom as a heteroatom. The heterocyclic compound may be amonocyclic compound (aliphatic monocyclic amine), or a polycycliccompound (aliphatic polycyclic amine).

Specific examples of the aliphatic monocyclic amine include piperidine,and piperazine.

The aliphatic polycyclic amine preferably has 6 to 10 carbon atoms, andspecific examples thereof include 1,5-diazabicyclo[4.3.0]-5-nonene,1,8-diazabicyclo[5.4.0]-7-undecene, hexamethylenetetramine, and1,4-diazabicyclo[2.2.2]octane.

Examples of other aliphatic amines includetris(2-methoxymethoxyethyl)amine, tris{2-(2-methoxyethoxy)ethyl}amine,tris{2-(2-methoxyethoxymethoxy)ethyl}amine,tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine,tris{2-(1-ethoxypropoxy)ethyl}amine andtris[2-{2-(2-hydroxyethoxy)ethoxy}ethyl]amine.

Examples of aromatic amines include aniline, pyridine,4-dimethylaminopyridine, pyrrole, indole, pyrazole, imidazole andderivatives thereof, as well as diphenylamine, triphenylamine andtribenzylamine.

These compounds can be used either alone, or in combinations of two ormore different compounds.

The component (D) is typically used in an amount within a range from0.01 to 5.0 parts by weight, relative to 100 parts by weight of thecomponent (A). When the amount of the component (D) is within theabove-mentioned range, the shape of the resist pattern and the postexposure stability of the latent image formed by the pattern-wiseexposure of the resist layer are improved.

Furthermore, in the resist composition of the present invention, forpreventing any deterioration in sensitivity, and improving the resistpattern shape and the post exposure stability of the latent image formedby the pattern-wise exposure of the resist layer, at least one compound(E) (hereafter referred to as “the component (E)”) selected from thegroup consisting of an organic carboxylic acid, or a phosphorus oxo acidor derivative thereof can be added.

Examples of suitable organic carboxylic acids include acetic acid,malonic acid, citric acid, malic acid, succinic acid, benzoic acid, andsalicylic acid.

Examples of phosphorus oxo acids include phosphoric acid, phosphonicacid and phosphinic acid. Among these, phosphonic acid is particularlydesirable.

Examples of oxo acid derivatives include esters in which a hydrogen atomwithin the above-mentioned oxo acids is substituted with a hydrocarbongroup. Examples of the hydrocarbon group include an alkyl group of 1 to5 carbon atoms and an aryl group of 6 to 15 carbon atoms.

Examples of phosphoric acid derivatives include phosphoric acid esterssuch as di-n-butyl phosphate and diphenyl phosphate.

Examples of phosphonic acid derivatives include phosphonic acid esterssuch as dimethyl phosphonate, di-n-butyl phosphonate, phenylphosphonicacid, diphenyl phosphonate and dibenzyl phosphonate.

Examples of phosphinic acid derivatives include phosphinic acid esterssuch as phenylphosphinic acid.

As the component (E), one type may be used alone, or two or more typesmay be used in combination.

The component (E) is typically used in an amount within a range from0.01 to 5.0 parts by weight, relative to 100 parts by weight of thecomponent (A).

If desired, miscible additives can also be added to the resistcomposition of the present invention. Examples of such miscibleadditives include additive resins for improving the performance of theresist film, surfactants for improving the applicability, dissolutioninhibitors, plasticizers, stabilizers, colorants, halation preventionagents, and dyes.

The resist composition of the present invention can be prepared bydissolving the materials for the resist composition in an organicsolvent (hereafter, frequently referred to as “component (S)”).

The component (S) may be any organic solvent which can dissolve therespective components to give a uniform solution, and one or more kindsof any organic solvent can be appropriately selected from those whichhave been conventionally known as solvents for a chemically amplifiedresist.

Examples thereof include lactones such as γ-butyrolactone;

ketones such as acetone, methyl ethyl ketone, cyclohexanone,methyl-n-pentyl ketone, methyl isopentyl ketone, and 2-heptanone;polyhydric alcohols, such as ethylene glycol, diethylene glycol,propylene glycol and dipropylene glycol;compounds having an ester bond, such as ethylene glycol monoacetate,diethylene glycol monoacetate, propylene glycol monoacetate, anddipropylene glycol monoacetate;polyhydric alcohol derivatives including compounds having an ether bond,such as a monoalkylether (e.g., monomethylether, monoethylether,monopropylether or monobutylether) or monophenylether of any of thesepolyhydric alcohols or compounds having an ester bond (among these,propylene glycol monomethyl ether acetate (PGMEA) and propylene glycolmonomethyl ether (PGME) are preferable);cyclic ethers such as dioxane; esters such as methyl lactate, ethyllactate (EL), methyl acetate, ethyl acetate, butyl acetate, methylpyruvate, ethyl pyruvate, methyl methoxypropionate, and ethylethoxypropionate;and aromatic organic solvents such as anisole, ethylbenzylether,cresylmethylether, diphenylether, dibenzylether, phenetole,butylphenylether, ethylbenzene, diethylbenzene, pentylbenzene,isopropylbenzene, toluene, xylene, cymene and mesitylene.

These solvents can be used individually, or in combination as a mixedsolvent.

Among these, propylene glycol monomethyl ether acetate (PGMEA),propylene glycol monomethyl ether (PGME), cyclohexanone and ethyllactate (EL) are preferable.

Further, among the mixed solvents, a mixed solvent obtained by mixingPGMEA with a polar solvent is preferable. The mixing ratio (weightratio) of the mixed solvent can be appropriately determined, taking intoconsideration the compatibility of the PGMEA with the polar solvent, butis preferably in the range of 1:9 to 9:1, more preferably from 2:8 to8:2. For example, when EL is mixed as the polar solvent, the PGMEA:ELweight ratio is preferably from 1:9 to 9:1, and more preferably from 2:8to 8:2. Alternatively, when PGME is mixed as the polar solvent, thePGMEA:PGME weight ratio is preferably from 1:9 to 9:1, more preferablyfrom 2:8 to 8:2, and still more preferably 3:7 to 7:3. Alternatively,when PGME and cyclohexanone is mixed as the polar solvent, thePGMEA:PGME and cyclohexanone weight ratio is preferably from 1:9 to 9:1,more preferably from 2:8 to 8:2, and still more preferably 3:7 to 7:3.

Further, as the component (S), a mixed solvent of one of PGMEA, EL, orthe mixed solvent of PGMEA and the polar solvent with γ-butyrolactone isalso preferable. The mixing ratio (former:latter) of such a mixedsolvent is preferably from 70:30 to 95:5.

The amount of the organic solvent is not particularly limited, and isappropriately adjusted to a concentration which enables coating of acoating solution to a substrate, depending on the thickness of thecoating film. In general, the organic solvent is used in an amount suchthat the solid content of the resist composition becomes within therange from 1 to 20% by weight, and preferably from 2 to 15% by weight.

The resist composition of the present invention exhibits excellentlithography properties such as exposure latitude (EL), roughness of theline width (line width roughness (LWR)) and the like and enablesformation of a resist pattern having an excellent shape.

In the present invention, the reasons why such effects can be achievedhave not been elucidated yet. However, since the component (A1)represents a polymeric compound, the structural unit (a5) constitutingthe component (A1) and having the structure —N(R^(a))—C(═O)—R^(b) on theside chain thereof can readily be uniformly distributed within theresist film. Therefore, during the formation of a resist pattern, aquenching effect in which the acid generated from the component (B) inthe exposed portions of the resist film is trapped can readily beuniformly obtained in the entire resist film. As a result, it ispresumed that since changing solubility of the component (A) atunexposed portions in a developing solution can be suppressed, sucheffects can be achieved.

In addition, the component (A1) exhibits high solubility in solvents fora chemically amplified resist, and exhibits excellent solubility inpropylene glycol monomethyl ether (PGME). As a result, according to aresist composition containing the component (A1), generation of defectsby developing can be suppressed.

It is presumed that since the component (A1) includes the structuralunit (a5) having an imide group on the side chain thereof, thecompatibility thereof with the solvent can be increased.

<<Method of Forming a Resist Pattern>>

The method of forming a resist pattern according to the presentinvention described above includes: forming a resist film on a substrateusing a resist composition of the present invention; conducting exposureof the resist film; and developing the resist film to form a resistpattern.

The method for forming a resist pattern according to the presentinvention can be performed, for example, as follows.

Firstly, the resist composition of the present invention is applied to asubstrate using a spinner or the like, and a bake treatment (postapplied bake (PAB)) is conducted at a temperature of 80 to 150° C. for40 to 120 seconds, preferably 60 to 90 seconds, to form a resist film.

Following selective exposure of the thus formed resist film, either byexposure through a mask having a predetermined pattern formed thereon(mask pattern) using an exposure apparatus such as an ArF exposureapparatus, an electron beam lithography apparatus or an EUV exposureapparatus, or by patterning via direct irradiation with an electron beamwithout using a mask pattern, baking treatment (post exposure baking(PEB)) is conducted under temperature conditions of 80 to 150° C. for 40to 120 seconds, and preferably 60 to 90 seconds.

Subsequently, the resulting resist film is subjected to developingtreatment.

For an alkali developing process, an alkali developing solution is usedin developing treatment. For a solvent developing process, a developingsolution containing an organic solvent (organic developing solution) isused in developing treatment.

After the developing treatment, it is preferable to perform rinsetreatment. In the case of an alkali developing process, the rinsetreatment is preferably a water rinse using pure water. In the case of asolvent developing process, it is preferable to use a rinse liquidcontaining an organic solvent.

In the case of a solvent developing process, after the developingtreatment or the rinse treatment, the developing solution or the rinseliquid remaining on the pattern can be removed by a treatment using asupercritical fluid.

After the developing treatment or the rinse treatment, drying isconducted. If desired, bake treatment (post bake) can be conductedfollowing the developing. In this manner, a resist pattern can beobtained.

The substrate is not specifically limited and a conventionally knownsubstrate can be used. For example, substrates for electroniccomponents, and such substrates having wiring patterns formed thereoncan be used. Specific examples of the material of the substrate includemetals such as silicon wafer, copper, chromium, iron and aluminum; andglass. Suitable materials for the wiring pattern include copper,aluminum, nickel, and gold.

Further, as the substrate, any one of the above-mentioned substratesprovided with an inorganic and/or organic film on the surface thereofmay be used. As the inorganic film, an inorganic antireflection film(inorganic BARC) can be used. As the organic film, an organicantireflection film (organic BARC) and an organic film such as alower-layer organic film used in a multilayer resist method can be used.

Here, a “multilayer resist method” is a method in which at least onelayer of an organic film (lower-layer organic film) and at least onelayer of a resist film (upper resist film) are provided on a substrate,and a resist pattern formed on the upper resist film is used as a maskto conduct patterning of the lower-layer organic film. This method isconsidered as being capable of forming a pattern with a high aspectratio. More specifically, in the multilayer resist method, a desiredthickness can be ensured by the lower-layer organic film, and as aresult, the thickness of the resist film can be reduced, and anextremely fine pattern with a high aspect ratio can be formed.

The multilayer resist method is broadly classified into a method inwhich a double-layer structure consisting of an upper-layer resist filmand a lower-layer organic film is formed (double-layer resist method),and a method in which a multilayer structure having at least threelayers consisting of an upper-layer resist film, a lower-layer organicfilm and at least one intermediate layer (thin metal film or the like)provided between the upper-layer resist film and the lower-layer organicfilm (triple-layer resist method).

The wavelength to be used for exposure is not particularly limited andthe exposure can be conducted using radiation such as ArF excimer laser,KrF excimer laser, F₂ excimer laser, extreme ultraviolet rays (EUV),vacuum ultraviolet rays (VUV), electron beam (EB), X-rays, and softX-rays. The resist composition of the present invention is effective toKrF excimer laser, ArF excimer laser, EB and EUV.

The exposure of the resist film can be either a general exposure (dryexposure) conducted in air or an inert gas such as nitrogen, orimmersion exposure (immersion lithography).

In immersion lithography, the region between the resist film and thelens at the lowermost point of the exposure apparatus is pre-filled witha solvent (immersion medium) that has a larger refractive index than therefractive index of air, and the exposure (immersion exposure) isconducted in this state.

The immersion medium preferably exhibits a refractive index larger thanthe refractive index of air but smaller than the refractive index of theresist film to be exposed. The refractive index of the immersion mediumis not particularly limited as long at it satisfies the above-mentionedrequirements.

Examples of this immersion medium which exhibits a refractive index thatis larger than the refractive index of air but smaller than therefractive index of the resist film include water, fluorine-based inertliquids, silicon-based solvents and hydrocarbon-based solvents.

Specific examples of the fluorine-based inert liquids include liquidscontaining a fluorine-based compound such as C₃HCl₂F₅, C₄F₉OCH₃,C₄F₉OC₂H₅ or C₅H₃F₇ as the main component, which have a boiling pointwithin a range from 70 to 180° C. and preferably from 80 to 160° C. Afluorine-based inert liquid having a boiling point within theabove-mentioned range is advantageous in that the removal of theimmersion medium after the exposure can be conducted by a simple method.

As a fluorine-based inert liquid, a perfluoroalkyl compound in which allof the hydrogen atoms of the alkyl group are substituted with fluorineatoms is particularly desirable. Examples of these perfluoroalkylcompounds include perfluoroalkylether compounds and perfluoroalkylaminecompounds.

Specifically, one example of a suitable perfluoroalkylether compound isperfluoro (2-butyl-tetrahydrofuran) (boiling point 102° C.), and anexample of a suitable perfluoroalkylamine compound isperfluorotributylamine (boiling point 174° C.).

As the immersion medium, water is preferable in terms of cost, safety,environment and versatility.

As examples of the alkali developing solution for developing treatmentin an alkali developing process, a 0.1 to 10% by weight aqueous solutionof tetramethylammonium hydroxide (TMAH) can be given.

As the organic solvent contained in the organic developing solution fordeveloping treatment in a solvent developing process, any of theconventional organic solvents can be used which are capable ofdissolving the component (A) (prior to exposure). Specific examples ofthe organic solvent include polar solvents such as ketone solvents,ester solvents, alcohol solvents, amide solvents and ether solvents, andhydrocarbon solvents.

If desired, the organic developing solution may have a conventionaladditive blended. Examples of the additive include surfactants. Thesurfactant is not particularly limited, and for example, an ionic ornon-ionic fluorine and/or silicon surfactant can be used.

When a surfactant is added, the amount thereof based on the total amountof the organic developing solution is generally 0.001 to 5% by weight,preferably 0.005 to 2% by weight, and more preferably 0.01 to 0.5% byweight.

The development treatment can be performed by a conventional developingmethod. Examples thereof include a method in which the substrate isimmersed in the developing solution for a predetermined time (a dipmethod), a method in which the developing solution is cast up on thesurface of the substrate by surface tension and maintained for apredetermined period (a puddle method), a method in which the developingsolution is sprayed onto the surface of the substrate (spray method),and a method in which the developing solution is continuously ejectedfrom a developing solution ejecting nozzle while scanning at a constantrate to apply the developing solution to the substrate while rotatingthe substrate at a constant rate (dynamic dispense method).

As the organic solvent contained in the rinse liquid used for rinsetreatment after the developing treatment in a solvent developingprocess, any of the aforementioned organic solvents for the organicdeveloping solution can be used which hardly dissolve the pattern. Ingeneral, at least one solvent selected from the group consisting ofhydrocarbon solvents, ketone solvents, ester solvents, alcohol solvents,amide solvents and ether solvents is used. Among these, at least onesolvent selected from the group consisting of hydrocarbon solvents,ketone solvents, ester solvents, alcohol solvents and amide solvents ispreferable, more preferably at least one solvent selected from the groupconsisting of alcohol solvents and ester solvents, and an alcoholsolvent is particularly desirable.

The rinse treatment (washing treatment) using the rinse liquid can beperformed by a conventional rinse method. Examples thereof include amethod in which the rinse liquid is continuously applied to thesubstrate while rotating it at a constant rate (rotational coatingmethod), a method in which the substrate is immersed in the rinse liquidfor a predetermined time (dip method), and a method in which the rinseliquid is sprayed onto the surface of the substrate (spray method).

<<Polymeric Compound>>

The polymeric compound of the present invention includes a structuralunit (a5) represented by general formula (a5-1) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; eachof R^(a) and R^(b) independently represents a hydrocarbon group whichmay have a substituent, and R^(a) and R^(b) may be mutually bonded toform a ring.

Preferable examples of the structural unit (a5) include structural unitsrepresented by general formula (a5-1-1) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; Xrepresents CH₂, CH₂CH₂, O, S or SO₂; each of R^(c) and R^(d)independently represents a hydrocarbon group which may have asubstituent or a hydrogen atom, and R^(c) and R^(d) may be mutuallybonded to form a ring; p represents an integer of 0 to 3.

The polymeric compound of the present invention preferably has, inaddition to the structural unit (a5), a structural unit (a1) derivedfrom an acrylate ester which may have the hydrogen atom bonded to thecarbon atom on the α-position substituted with a substituent andcontaining an acid decomposable group which exhibits increased polarityby the action of acid.

Further, the polymeric compound of the present invention preferablyincludes, in addition to the structural unit (a5) and the structuralunit (a1), at least one structural unit selected from the groupconsisting of a structural unit (a0) derived from an acrylate esterwhich may have the hydrogen atom bonded to the carbon atom on theα-position substituted with a substituent and contains an —SO₂—containing cyclic group and a structural unit (a2) derived from anacrylate ester which may have the hydrogen atom bonded to the carbonatom on the α-position substituted with a substituent and contains alactone-containing cyclic group.

Furthermore, it is preferable that the polymeric compound of the presentinvention include a structural unit (a3) derived from an acrylate esterwhich may have the hydrogen atom bonded to the carbon atom on theα-position substituted with a substituent and contains a polargroup-containing aliphatic hydrocarbon group and, as well as thestructural unit (a5) and the structural unit (a1), or the structuralunit (a5), the structural unit (a1) and at least one structural unitselected from the group consisting of the structural unit (a0) and thestructural unit (a2).

The explanation of the polymeric compound of the present invention isthe same as the explanation of the component (A1) of the resistcomposition of the present invention described above.

EXAMPLES

A description of examples of the present invention follows, although thescope of the present invention is by no way limited by these examples.

In the following examples, a unit represented by a chemical formula (1)is referred to as “compound (1)”, and the same applies for compoundsrepresented by other formulas.

In the NMR analysis, the internal standard for ¹H-NMR and ¹³C-NMR wastetramethylsilane (TMS). The internal standard for ¹⁹F-NMR washexafluorobenzene (provided that the peak of hexafluorobenzene wasregarded as −160 ppm).

Monomer Synthesis Example 1 Synthesis of Compound (6)

The compound (6) used in the polymer synthesis examples described laterwas synthesized as follows.

300 mL of a THF solution containing 20 g (105.14 mmol) of an alcohol(6), 30.23 g (157.71 mmol) of ethyldiisopropylaminocarbodiimide (EDCI)hydrochloride and 0.6 g (5 mmol) of dimethylaminopyridine (DMAP) wasadded to a 500 mL three-necked flask in a nitrogen atmosphere, and 16.67g (115.66 mmol) of a precursor (6) was added thereto while cooling withice (0° C.), followed by stirring at room temperature for 12 hours.

After conducting thin-layer chromatography (TLC) to confirm that the rawmaterials had dissipated, 50 mL of water was added to stop the reaction.Then, the reaction solvent was concentrated under reduced pressure, andextraction was conducted with ethyl acetate three times. The obtainedorganic phase was washed with water, saturated sodium hydrogencarbonateand 1N—HClaq in this order. Thereafter, the solvent was distilled offunder reduced pressure, and the resulting product was dried, therebyobtaining the compound (6).

The results of NMR analysis of the obtained compound (6) were asfollows.

¹H-NMR (CDCl₃, 400 MHz): δ(ppm)=6.22 (s, 1H, H^(a)), 5.70 (s, 1H,H^(b)), 4.71-4.85 (m, 2H, H^(c,d)), 4.67 (s, 2H, H^(k)), 3.40-3.60 (m,2H, H^(e,f)), 2.58-2.70 (m, 1H, H^(g)), 2.11-2.21 (m, 2H, H^(h)), 2.00(s, 3H, H^(i)), 1.76-2.09 (m, 2H, H^(j)).

Polymer Synthesis Example 1 Synthesis of Polymeric Compound 1

In a separable flask equipped with a thermometer, a reflux tube and anitrogen feeding pipe, 12.00 g (70.52 mmol) of the compound (1), 9.97 g(40.63 mmol) of a compound (2), 17.88 g (68.13 mmol) of a compound (3),5.63 g (33.47 mmol) of a compound (4) and 6.21 g (26.32 mmol) of acompound (5) were dissolved in 66.42 g of methyl ethyl ketone (MEK) toobtain a solution. Then, 11.95 mmol of dimethyl 2,2′-azobis(isobutyrate)(V-601) was added and dissolved in the obtained solution.

The resultant was dropwise added to 36.03 g of MEK heated to 80° C. in anitrogen atmosphere over 3 hours. Thereafter, the reaction solution washeated for 2 hour while stirring, and then cooled to room temperature.

The obtained reaction polymer solution was dropwise added to an excessamount of a mixed solvent of n-heptane/isopropanol=90/10 (weight ratio),and an operation to deposit a polymer was conducted. Thereafter, theprecipitated white powder was separated by filtration, followed bywashing with a methanol and drying, thereby obtaining 32.49 g of apolymeric compound 1 as an objective compound.

With respect to the polymeric compound 1, the weight average molecularweight (Mw) and the dispersity (Mw/Mn) were determined by thepolystyrene equivalent value as measured by gel permeationchromatography (GPC). As a result, it was found that the weight averagemolecular weight was 6,700, and the dispersity was 1.56.

Further, as a result of an analysis by carbon 13 nuclear magneticresonance spectroscopy (600 MHz, ¹³C-NMR), it was found that thecomposition of the copolymer (ratio (molar ratio) of the respectivestructural units within the structural formula) wasl/m/n/o/p=37.0/15.3/17.8/16.0/13.9.

Polymer Synthesis Examples 2 to 8 Synthesis of Polymeric Compounds 2 to8

Polymeric compounds 2 to 8 were synthesized in the same manner as inPolymer Synthesis Example 1, except that the following compounds (1) to(8) which derived the structural units constituting each polymericcompound were used in predetermined molar ratio.

With respect to each polymeric compound, the compounds which derivedeach structural unit, the composition of the copolymer analyzed bycarbon 13 nuclear magnetic resonance spectroscopy (600 MHz, ¹³C-NMR),the weight average molecular weight and the dispersity (Mw/Mn)determined by the polystyrene equivalent value as measured by gelpermeation chromatography (GPC) are shown in Table 1.

TABLE 1 Compound which derived each Composition of Mw/ structural unitCopolymer Mw Mn Polymeric (1)/(2)/(3)/(4)/(5) 37.0/15.3/17.8/ 6700 1.56Compound 1 16.0/13.9 Polymeric (6)/(3)/(2) 42.0/35.4/22.6 5600 1.52Compound 2 Polymeric (2)/(3)/(7) 33.3/12.0/54.7 4600 1.58 Compound 3Polymeric (2)/(3)/(8)/(5) 36.5/34.1/18.9/10.5 8200 1.61 Compound 4Polymeric (1)/(6)/(3)/(4)/(5) 34.7/21.7/16.3/ 7900 1.57 Compound 514.8/12.5 Polymeric (6)/(3)/(5) 39.4/39.9/20.7 6000 1.42 Compound 6Polymeric (6)/(3)/(7) 40.0/10.8/49.2 6100 1.61 Compound 7 Polymeric(6)/(3)/(8)/(5) 38.5/37.9/14.6/9.0 6400 1.55 Compound 8

Preparation of Resist Composition Examples 1 to 4, Comparative Examples1 to 4

The components shown in Table 2 were mixed together and dissolved toobtain resist compositions.

TABLE 2 Com- Com- Com- Com- ponent ponent ponent ponent (A) Component(B) (D) (E) (S) Example 1 (A)-1 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 [100][8.81] [3.11] [0.38] [0.47] [2700] Comparative (A)-2 (B)-1 (B)-2 (D)-1(E)-1 (S)-1 Example 1 [100] [8.81] [3.11] [0.38] [0.47] [2700] Example 2(A)-3 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 [100] [8.81] [3.11] [0.38] [0.47][2700] Comparative (A)-4 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 Example 2 [100][8.81] [3.11] [0.38] [0.47] [2700] Example 3 (A)-5 (B)-1 (B)-2 (D)-1(E)-1 (S)-1 [100] [8.81] [3.11] [0.38] [0.47] [2700] Comparative (A)-6(B)-1 (B)-2 (D)-1 (E)-1 (S)-1 Example 3 [100] [8.81] [3.11] [0.38][0.47] [2700] Example 4 (A)-7 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 [100] [8.81][3.11] [0.38] [0.47] [2700] Comparative (A)-8 (B)-1 (B)-2 (D)-1 (E)-1(S)-1 Example 4 [100] [8.81] [3.11] [0.38] [0.47] [2700]

In Table 2, the values in brackets [ ] indicate the amount (in terms ofparts by weight) of the component added. Further, the referencecharacters indicate the following.

(A)-1: the aforementioned polymeric compound 1

(A)-2: the aforementioned polymeric compound 5

(A)-3: the aforementioned polymeric compound 2

(A)-4: the aforementioned polymeric compound 6

(A)-5: the aforementioned polymeric compound 3

(A)-6: the aforementioned polymeric compound 7

(A)-7: the aforementioned polymeric compound 4

(A)-8: the aforementioned polymeric compound 8

(B)-1: a compound represented by chemical formula (B)-1 shown below

(B)-2: a compound represented by chemical formula (B)-2 shown below

(D)-1: tri-n-pentylamine

(E)-1: salicylic acid

(S)-1: a mixed solvent of PGMEA/PGME (60/40 by weight ratio)

<Formation of Resist Pattern>

An organic anti-reflection film composition (product name: ARC29,manufactured by Brewer Science Ltd.) was applied to an 8-inch siliconwafer using a spinner, and the composition was then baked at 205° C. for60 seconds, thereby forming an organic anti-reflection film having afilm thickness of 77 nm.

Then, each of the resist compositions obtained above was applied to theorganic anti-reflection film using a spinner, and was then prebaked(PAB) on a hotplate at a PAB temperature indicated in Table 3 for 60seconds and dried, thereby forming a resist film having a film thicknessof 120 nm.

Subsequently, the resist film was selectively irradiated with an ArFexcimer laser (193 nm) through a mask pattern (6% halftone mask), usingan ArF exposure apparatus NSR-S302A (manufactured by Nikon Corporation,NA (numerical aperture)=0.60, 2/3 annular illumination).

Thereafter, a post exposure bake (PEB) treatment was conducted at a PABtemperature indicated in Table 3 for 60 seconds, followed by alkalidevelopment for 30 seconds at 23° C. in a 2.38% by weight aqueoussolution of TMAH (product name: NMD-3; manufactured by Tokyo Ohka KogyoCo., Ltd.). Then, the resist was washed for 30 seconds with pure water,further followed by conducting a bake treatment (post bake) at 100° C.for 60 seconds.

As a result, in each of the examples, a 1:1 line and space pattern (L/Spattern) having a line width of 130 nm and a pitch of 260 nm was formedon the resist film. The optimal exposure dose Eop (mJ/cm²) wasdetermined. The results are shown in Table 3.

[Evaluation of Exposure Latitude (EL)]

With respect to the above Eop, the exposure dose with which an L/Spattern having a dimension of the target dimension (line width: 130nm)±5% (i.e., 123.5 nm to 136.5 nm) was determined, and the EL (unit: %)was determined by the following formula. The results are shown in Table3.

EL(%)=(|E1−E2|/Eop)×100

In the formula, E1 represents the exposure dose (mJ/cm²) for forming anL/S pattern having a space width of 123.5 nm, and E2 represents theexposure dose (mJ/cm²) for forming an L/S pattern having a space widthof 136.5 nm.

The larger the value of the “EL”, the smaller the change in the patternsize by the variation of the exposure dose.

[Evaluation of Line Width Roughness (LWR)]

With respect to each of the 1:1 L/S patterns, which have a line width of130 nm and a pitch of 260 nm, formed with the above Eop, the space widthat 5 points in the lengthwise direction of the space was measured usinga measuring scanning electron microscope (SEM) (product name: S-9220,manufactured by Hitachi, Ltd.; acceleration voltage: 800V), and from theresults, the value of 3 times the standard deviation s (i.e., 3 s) wascalculated as a yardstick of LWR. The results are shown in Table 3.

The smaller this 3 s value is, the lower the level of roughness of theline width, indicating that an L/S pattern with a uniform width wasobtained.

TABLE 3 PAB PEB Eop EL LWR (° C.) (° C.) (mJ/cm²) (%) (nm) Example 1 10595 32.1 8.96 8.51 Comparative 105 95 22.2 8.54 10.75 Example 1 Example 2100 90 31.5 7.39 8.23 Comparative 100 90 25.0 7.02 9.22 Example 2Example 3 80 80 34.5 7.78 7.18 Comparative 80 80 27.1 6.34 8.49 Example3 Example 4 80 80 37.4 8.44 7.44 Comparative 80 80 29.8 7.51 8.93Example 4

From the results shown in Table 3, it was confirmed that the resistcompositions of Examples 1 to 4 according to the present invention weresuperior to the resist compositions of Comparative Examples 1 to 4corresponding to each of Examples 1 to 4 in that they exhibitedexcellent lithography properties and enabled formation of a resistpattern having an excellent shape, since the value of the EL thereof islarger and the value of the LWR thereof is small.

<Solubility of Base Component (A) in Organic Solvent>

Using polymeric compounds and organic solvents shown below, to becomeeach solution in which the concentration of the polymeric compound is 1%by weight and 20% by weight, when each organic solvent was added to eachpolymeric compound and was mixed, it was evaluated whether eachpolymeric compound was dissolved in each organic solvent at roomtemperature (23° C.) or not.

Polymeric compound: the aforementioned polymeric compound 1 and theaforementioned polymeric compound 5

Organic solvent: propylene glycol monomethyl ether acetate, propyleneglycol monomethyl ether and cyclohexanone

The obtained evaluation results are shown in Table 4.

In Table, “A” indicates that the polymeric compound was dissolved assoon as mixing, “B” indicates that the polymeric compound was dissolvedin long mixing time (for 30 minutes or more), “C” indicates that thepolymeric compound was not dissolved, and “-” indicates no example.

TABLE 4 Polymeric Compound 5 Polymeric Compound 1 1% by 20% by 1% by 20%by Organic Solvent weight weight weight weight Propylene Glycol — B — AMonomethyl Ether Acetate Propylene Glyco C C — A Monomethyl EtherCyclohexanone — A — A

From the results shown in Table 4, it was confirmed that the polymericcompound 1 of the present invention including a structural unit (a5)exhibited high solubility in each of the organic solvents.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

1. A resist composition comprising a base component (A) which exhibitschanged solubility in a developing solution under action of acid and anacid-generator component (B) which generates acid upon exposure, whereinthe base component (A) comprises a polymeric compound (A1) having astructural unit (a5) represented by general formula (a5-1) shown below:

wherein R represents a hydrogen atom, an alkyl group of 1 to 5 carbonatoms or a halogenated alkyl group of 1 to 5 carbon atoms; each of R^(a)and R^(b) independently represents a hydrocarbon group which may have asubstituent, and R^(a) and R^(b) may be mutually bonded to form a ring.2. A resist composition according to claim 1, wherein the structuralunit (a5) is a structural unit represented by general formula (a5-1-1)shown below:

wherein R represents a hydrogen atom, an alkyl group of 1 to 5 carbonatoms or a halogenated alkyl group of 1 to 5 carbon atoms; X representsCH₂, CH₂CH₂, O, S or SO₂; each of R^(c) and R^(d) independentlyrepresents a hydrocarbon group which may have a substituent or ahydrogen atom, and R^(c) and R^(d) may be mutually bonded to form aring; p represents an integer of 0 to
 3. 3. A resist compositionaccording to claim 1, wherein the polymeric compound (A1) furthercomprises a structural unit (a1) derived from an acrylate ester whichmay have the hydrogen atom bonded to the carbon atom on the α-positionsubstituted with a substituent and containing an acid decomposable groupwhich exhibits increased polarity by the action of acid.
 4. A resistcomposition according to claim 3, wherein the polymeric compound (A1)further comprises at least one structural unit selected from the groupconsisting of a structural unit (a0) derived from an acrylate esterwhich may have the hydrogen atom bonded to the carbon atom on theα-position substituted with a substituent and contains an —SO₂—containing cyclic group and a structural unit (a2) derived from anacrylate ester which may have the hydrogen atom bonded to the carbonatom on the α-position substituted with a substituent and contains alactone-containing cyclic group.
 5. A resist composition according toclaim 3, wherein the polymeric compound (A1) further comprises astructural unit (a3) derived from an acrylate ester which may have thehydrogen atom bonded to the carbon atom on the α-position substitutedwith a substituent and contains a polar group-containing aliphatichydrocarbon group.
 6. A method of forming a resist pattern, comprising:using a resist composition according to any one of claims 1 to 5 to forma resist film on a substrate; conducting exposure of the resist film;and developing the resist film to form a resist pattern.
 7. A polymericcompound comprising a structural unit (a5) represented by generalformula (a5-1) shown below:

wherein R represents a hydrogen atom, an alkyl group of 1 to 5 carbonatoms or a halogenated alkyl group of 1 to 5 carbon atoms; each of R^(a)and R^(b) independently represents a hydrocarbon group which may have asubstituent, and R^(a) and R^(b) may be mutually bonded to form a ring.8. A polymeric compound according to claim 7, wherein the structuralunit (a5) is a structural unit represented by general formula (a5-1-1)shown below:

wherein R represents a hydrogen atom, an alkyl group of 1 to 5 carbonatoms or a halogenated alkyl group of 1 to 5 carbon atoms; X representsCH₂, CH₂CH₂, O, S or SO₂; each of R^(c) and R^(d) independentlyrepresents a hydrocarbon group which may have a substituent or ahydrogen atom, and R^(e) and R^(d) may be mutually bonded to form aring; p represents an integer of 0 to
 3. 9. A polymeric compoundaccording to claim 7, further comprising a structural unit (a1) derivedfrom an acrylate ester which may have the hydrogen atom bonded to thecarbon atom on the α-position substituted with a substituent andcontaining an acid decomposable group which exhibits increased polarityby the action of acid.
 10. A polymeric compound according to claim 9,further comprising at least one structural unit selected from the groupconsisting of a structural unit (a0) derived from an acrylate esterwhich may have the hydrogen atom bonded to the carbon atom on theα-position substituted with a substituent and contains an —SO₂—containing cyclic group and a structural unit (a2) derived from anacrylate ester which may have the hydrogen atom bonded to the carbonatom on the α-position substituted with a substituent and contains alactone-containing cyclic group.
 11. A polymeric compound according toclaim 9 or claim 10, further comprising a structural unit (a3) derivedfrom an acrylate ester which may have the hydrogen atom bonded to thecarbon atom on the α-position substituted with a substituent andcontains a polar group-containing aliphatic hydrocarbon group.